Gas diffusion electrodes and related articles, systems, and methods

Abstract

Gas diffusion electrodes and related articles, systems, and methods are generally described herein.

Description

[0001] GAS DIFFUSION ELECTRODES AND RELATED ARTICLES, SYSTEMS, AND METHODS

[0002] RELATED APPLICATIONS

[0003] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 520,052, filed August 16, 2023, and entitled “Gas Diffusion Electrodes and Related Articles, Systems, and Methods,” which is incorporated herein by reference in its entirety for all purposes.

[0004] TECHNICAL FIELD

[0005] Gas diffusion electrodes and related articles, systems, and methods are generally described herein.

[0006] BACKGROUND

[0007] Electrochemical CO2 reduction has seen an increase in attention for its promise to convert captured CO2 into a variety of useful fuels, chemicals, and products otherwise produced from petrochemicals. When paired with renewable electricity, CO2 conversion can serve as a means for energy storage or enable net-negative sequestration of CO2 in durable products. Over the last decade, progress in developing novel catalysts, reaction pathways, and electrode architectures have collectively pushed electrochemical CO2 conversion towards commercial relevance. To realize commercial relevance, however, the electrodes and their supporting systems should be scaled to large sizes.

[0008] SUMMARY

[0009] The present disclosure is generally directed to gas diffusion electrodes and related articles, systems, and methods. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0010] According to some embodiments, a composite article is described. In certain embodiments, the composite article comprises a hydrophobic material having a water contact angle of greater than or equal to 90°, a catalyst material, and an electrically conductive material having an electrical conductivity of greater than or equal to 104S / m. In some embodiments, the electrically conductive material occupies less than or equal to 5% of a surface area of the catalyst material. In certain embodiments, an electrode is described. In some embodiments, the electrode comprises a catalyst layer having a first surface and a second surface, wherein the first surface is substantially opposite the second surface, a gas diffusion layer disposed on the second surface of the catalyst layer, and an electrically conductive material. According to certain embodiments, at least a portion of the electrically conductive material is configured to be in electrical communication with a current collector such that the electrically conductive material provides an electrically conductive pathway from the current collector to the first surface of the catalyst layer. In some embodiments, the electrode has a geometric area greater than or equal to 5 cm2.

[0011] According to certain embodiments, a catalytic, aqueous barrier, gas diffusion electrode is described. In some embodiments, the catalytic, aqueous barrier, gas diffusion electrode comprises: a hydrophobic gas diffusion layer configured to provide a substantial barrier to transport of an electrolyte across the electrode from a first surface of the electrode to a second surface of the electrode, wherein the second surface of the electrode is substantially opposite the first surface, and wherein the electrode has a gas permeability of at least 0.05 ftVmin ft2at 125 Pa across at least a portion of the electrode and a water entry pressure of less than 100 psi across at least a portion of the electrode; a catalyst material configured to be exposed to the electrolyte in contact with the first surface of the electrode; and an electrically conductive material configured to provide electronic conductivity to at least some of the catalyst material, wherein the catalyst material is configured to be in contact with a gas in the electrolyte in contact with the first surface of the electrode, the electrically conductive material configured to be in electrical communication with a current collector in contact with the second surface of the electrode such that the electrically conductive material provides an electrically conductive pathway from the current collector to the catalyst material.

[0012] Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

[0014] FIG. 1 A shows, according to some embodiments, a cross-sectional schematic diagram of a composite article.

[0015] FIG. IB shows, according to some embodiments, a top-view schematic diagram of the composite article shown in FIG. 1 A.

[0016] FIG. 2A shows, according to some embodiments, a cross-sectional schematic diagram of another composite article.

[0017] FIG. 2B shows, according to some embodiments, a top-view schematic diagram of the composite article shown in FIG. 2A.

[0018] FIG. 3 A shows, according to some embodiments, a cross-sectional schematic diagram of yet another composite article.

[0019] FIG. 3B shows, according to some embodiments, a top-view schematic diagram of the composite article shown in FIG. 3 A.

[0020] FIG. 4A shows, according to some embodiments, a cross-sectional schematic diagram of an electrochemical cell comprising the composite article shown in FIGS. 1 A-1B.

[0021] FIG. 4B shows, according to some embodiments, a cross-sectional schematic diagram of an electrochemical cell comprising the composite article shown in FIGS. 2A-2B.

[0022] FIG. 4C shows, according to some embodiments, a cross-sectional schematic diagram of an electrochemical cell comprising the composite article shown in FIGS. 3A-3B.

[0023] FIG. 5A shows, according to some embodiments, a schematic diagram of triple phase contact between gaseous carbon dioxide (CO2), an electrolyte, and a solid catalyst.

[0024] FIG. 5B shows, according to some embodiments, a schematic diagram of a gas diffusion electrode that maintains the triple phase contact shown in FIG. 5 A.

[0025] FIG. 6A shows, according to some embodiments, a schematic diagram of a conventional flooding-prone, conductive carbon paper gas diffusion electrode and its effect on ohmic overpotential (AF). FIG. 6B shows, according to some embodiments, a schematic diagram of a conventional insulating expanded polytetrafluoroethylene (ePTFE) gas diffusion electrode and its effect on AE

[0026] FIG. 6C shows, according to some embodiments, a schematic diagram of a hierarchically conductive gas diffusion electrode (HCGDE) and its effect on AF.

[0027] FIG. 7 shows, according to some embodiments, the faradaic efficiency (FE) of ethylene (C2H4) and hydrogen gas (EE) as a function of time for a conventional carbon paper gas diffusion electrode.

[0028] FIG. 8 shows, according to some embodiments, the FE of C2H4 and the voltage as a function of current density for a conventional ePTFE gas diffusion electrode.

[0029] FIG. 9 shows, according to some embodiments, the intrinsic material tradeoff between conductivity and hydrophobicity for a conventional carbon paper gas diffusion electrode and an ePTFE gas diffusion electrode, with a HCGDE possessing both hydrophobicity and conductivity.

[0030] FIG. 10 shows, according to some embodiments, top-view and cross-sectional schematic diagrams of some exemplary embodiments of HCGDEs.

[0031] FIG. 11 A shows, according to some embodiments, a simulated voltage field on a 4.2 cm2square electrode at 250 mA / cm2with 0 V defined as the lowest voltage on the surface.

[0032] FIG. 1 IB shows, according to some embodiments, a simulated C2H4 FE field due to voltage gradients.

[0033] FIG. 12A shows, according to some embodiments, an ohmic loss model predicting the voltage shift and decrease in FE occurring at a 4.2 cm2electrode.

[0034] FIG. 12B shows, according to some embodiments, a simulation model predicting the i-V curve for a 4.2 cm2electrode.

[0035] FIG. 12C shows, according to some embodiments, an ohmic loss model predicting the voltage shift and decrease in FE occurring at a 2.5 cm2electrode.

[0036] FIG. 12D shows, according to some embodiments, a simulation model predicting the i-V curve for a 2.5 cm2electrode.

[0037] FIG. 13 A shows, according to some embodiments, a simulated current density distribution for an electrode with a characteristic spacing of 10 millimeters.

[0038] FIG. 13B shows, according to some embodiments, a simulated C2H4 FE model for an electrode with a characteristic spacing of 10 millimeters.

[0039] FIG. 14 shows, according to some embodiments, the maximum average electrical efficiency in unit cell simulations at various spacings. FIG. 15A shows, according to some embodiments, a photograph of the catalyst side of a sewn-HCGDE with an active area of 4.2 cm2and characteristic spacing of 4 millimeters.

[0040] FIG. 15B shows, according to some embodiments, a photograph of the gas diffusion side of the sewn-HCGDE shown in FIG. 15 A.

[0041] FIG. 16A shows, according to some embodiments, the full cell voltage of a 4.2 cm2HCGDE as compared to bare conventional ePTFE gas diffusion electrodes without hierarchical conductors.

[0042] FIG. 16B shows, according to some embodiments, the C2H4 FE for a 4.2 cm2HCGDE as compared to bare conventional ePTFE gas diffusion electrodes without hierarchical conductors.

[0043] FIG. 17 shows, according to some embodiments, a long-term stability test of a HCGDE as compared to a carbon paper gas diffusion electrode.

[0044] FIG. 18 shows, according to some embodiments, a photograph of flowfields that can accommodate a 5 cm2electrode and a 50 cm2electrode.

[0045] FIG. 19 shows, according to some embodiments, the estimated capital expenditure (CAPEX) costs of a cell stack of CO2R electrolyzers as a function of their current density.

[0046] FIG. 20A shows, according to some embodiments, a schematic diagram of an electrode which is electrically connected from the left side only, causing a voltage gradient across the electrode.

[0047] FIG. 20B shows, according to some embodiments, the faradaic gas fraction measured in the three product streams shown in FIG. 20A.

[0048] FIG. 21 shows, according to some embodiments, a schematic diagram of wire- HCGDE with wires of diameter, c that pierce the membrane to reach the catalyst.

[0049] FIG. 22 shows, according to some embodiments, a simulation of a unit cell at a voltage of 3.6 V, with two current sinks that replicate the effect of conductive wires at .s = 8 millimeters.

[0050] FIG. 23 shows, according to some embodiments, the C2+ FE of HCGDE electrodes with sizes ranging from 4.2 cm2to 50 cm2.

[0051] FIG. 24A shows, according to some embodiments, the C2H4 FE of a 50 cm2HCGDE as compared to modeled ePTFE gas diffusion electrodes.

[0052] FIG. 24B shows, according to some embodiments, the current density of a 50 cm2HCGDE as compared to modeled ePTFE gas diffusion electrodes. DETAILED DESCRIPTION

[0053] Composite materials and related articles, systems, and methods are generally described herein. According to some embodiments, a composite article is described. The composite article may comprise am electrically insulating, hydrophobic material (e.g., having a water contact angle of greater than or equal to 90° and less than or equal to 180°), a catalyst material, and an electrically conductive material (e.g., having an electrical conductivity of greater than or equal to 104S / m and less than or equal to 108S / m).

[0054] The composite article may be configured as an electrode (e.g., a gas diffusion electrode) comprising a gas diffusion layer, a catalyst layer, and the electrically conductive material. In some embodiments, for example, the hydrophobic material may be configured as the gas diffusion layer. The gas diffusion layer may provide a pathway for transport of one or more gases (e.g., CO2, N2) across at least a portion of the electrode while also providing a substantial barrier for transport of an electrolyte (e.g., water or an aqueous solution) across at least a portion of the electrode. The catalyst material may be configured as the catalyst layer. The catalyst layer may be in contact with the gas diffusion layer and configured to catalyze a conversion (e.g., reduction) of one or more gases into one or more products. The electrically conductive material may be configured to be in electrical communication with a source of electrons (e.g., a current collector) such that the electrically conductive material provides an electrically conductive pathway from the source of electrons to the catalyst layer. The electrically conductive pathway may pass through the bulk of the gas diffusion layer (e.g., through a thickness of the gas diffusion layer), through the bulk of the catalyst layer (e.g., through a thickness of the catalyst layer), and / or along a surface of the catalyst layer.

[0055] Conventionally, there exists a negative correlation between hydrophobicity and conductivity for materials used in gas diffusion electrodes, i.e., highly conductive materials tend to be hydrophilic, while hydrophobic materials tend to be nonconductive. Carbon paper, for example, has good conductivity and scalability, but is susceptible to losing hydrophobicity during electrochemical cell operation due to flooding events in which the electrolyte impregnates the carbon paper. Alternatively, expanded polytetrafluoroethylene has a robust hydrophobicity but a conductivity on the order of 10'16S / m, leading to significant ohmic losses upon scaling to industry-relevant electrode sizes. In contrast, the gas diffusion electrodes described herein advantageously possess adequate electronic conductivity to facilitate electronic transfer via the electrically conductive material to the catalyst layer with minimal ohmic loss while also maintaining robust hydrophobicity to ensure that a triple phase contact between gas (e.g., CO2, N2), liquid (e.g., electrolyte), and solid (e.g., catalyst) is sustained at the catalyst layer, even after long periods of electrochemical cell operation. Such a configuration allows the gas diffusion electrode to be scaled to industry -relevant sizes. As would be recognizable by a person of ordinary skill in the art, the physical design of the gas diffusion electrode described herein is universal and advantageously compatible with any number of hydrophobic materials (e.g., hydrophobic polymers), catalyst materials (e.g., catalytic metals), and electrically conductive materials (e.g., electrically conductive metals).

[0056] Also described herein is a method of electrochemically converting (e.g., reducing) one or more gases (e.g., CO2, N2) to one or more products. In some embodiments, for example, an electrochemical cell comprising the gas diffusion electrode is employed to convert the one or more gases to the one or more products at high faradaic efficiencies and low cell voltages at commercially relevant current densities.

[0057] According to certain embodiments, the composite article comprises a hydrophobic material. FIG. 1 A shows, according to some embodiments, a cross-sectional schematic diagram of composite article 100a. FIG. IB shows, according to some embodiments, a topview schematic diagram of composite article 100a. The cross-section shown in FIG. 1 A is taken along dotted line 1 A in FIG. IB. Referring to FIG. 1 A, composite article 100a comprises hydrophobic material 102. As explained in greater detail herein, hydrophobic material 102 is hidden from view in FIG. IB by catalyst material 104.

[0058] The hydrophobic material may have any of a variety of suitable water contact angles. In some embodiments, for example, the hydrophobic material has a water contact angle of greater than or equal to 90°, greater than or equal to 95°, greater than or equal to 100°, greater than or equal to 105°, greater than or equal to 110°, greater than or equal to 115°, greater than or equal to 120°, greater than or equal to 125°, greater than or equal to 130°, greater than or equal to 135°, greater than or equal to 140°, greater than or equal to 145°, greater than or equal to 150°, greater than or equal to 155°, greater than or equal to 160°, greater than or equal to 165°, greater than or equal to 170°, or greater than or equal to 175°. In certain embodiments, the hydrophobic material has a water contact angle of less than or equal to 180°, less than or equal to 175°, less than or equal to 170°, less than or equal to 165°, less than or equal to 160°, less than or equal to 155°, less than or equal to 150°, less than or equal to 145°, less than or equal to 140°, less than or equal to 135°, less than or equal to 130°, less than or equal to 125°, less than or equal to 120°, less than or equal to 115°, less than or equal to 110°, less than or equal to 105°, less than or equal to 100°, or less than or equal to 95°. Combinations of the above recited ranges are possible (e.g., the hydrophobic material has a water contact angle of greater than or equal to 90° and less than or equal to 180°, the hydrophobic material has a water contact angle of greater than or equal to 135° and less than or equal to 140°). Other ranges are also possible. In some embodiments, the water contact angle of the hydrophobic material may be determined by a goniometer.

[0059] According to certain embodiments, the hydrophobic material is configured as a layer. Referring to FIG. 1 A, for example, hydrophobic material 102 is configured as a layer. In some embodiments, the layer of the hydrophobic material comprises a first surface and a second surface that is substantially opposite the first surface. As shown, for example, in FIG. 1A, the layer of hydrophobic material 102 comprises first surface 108a and second surface 110a that is substantially opposite first surface 108a.

[0060] The layer of the hydrophobic material may have any of a variety of suitable thicknesses. For example, referring to FIG. 1A, the layer of hydrophobic material 102 has thickness 112a. In some embodiments, the layer of the hydrophobic material has a thickness greater than or equal to 1 micrometer, greater than or equal to 5 micrometers, greater than or equal to 10 micrometers, greater than or equal to 50 micrometers, greater than or equal to 100 micrometers, greater than or equal to 200 micrometers, greater than or equal to 300 micrometers, greater than or equal to 400 micrometers, greater than or equal to 500 micrometers, greater than or equal to 600 micrometers, greater than or equal to 700 micrometers, greater than or equal to 800 micrometers, or greater than or equal to 900 micrometers. In certain embodiments, the layer of the hydrophobic material has a thickness less than or equal to 1 millimeter, less than or equal to 900 micrometers, less than or equal to 800 micrometers, less than or equal to 700 micrometers, less than or equal to 600 micrometers, less than or equal to 500 micrometers, less than or equal to 400 micrometers, less than or equal to 300 micrometers, less than or equal to 200 micrometers, less than or equal to 100 micrometers, less than or equal to 50 micrometers, less than or equal to 10 micrometers, or less than or equal to 5 micrometers. Combinations of the above recited ranges are possible (e.g., the layer of the hydrophobic material has a thickness greater than or equal to 1 micrometer and less than or equal to 1 millimeter, the layer of the hydrophobic material has a thickness greater than or equal to 300 micrometers and less than or equal to 400 micrometers). Other ranges are also possible. In certain embodiments, the thickness of the layer of the hydrophobic material is determined by microscopy (e.g., scanning electron microscopy (SEM)).

[0061] While the layer of hydrophobic material 102 is depicted in FIG. 1 A as a smooth layer of uniform thickness, those of ordinary skill in the art would understand that this is for illustration purposes only and the thickness of the layer of the hydrophobic material may have a particular roughness and / or may vary in thickness, in accordance with some embodiments. In certain embodiments, the layer of hydrophobic material may be of relatively uniform thickness (e.g., within less than or equal to 10% of the total thickness) over at least a substantial portion of the layer of the hydrophobic material (e.g., greater than or equal to 75% of the surface area of the layer of the hydrophobic material).

[0062] In certain embodiments, the hydrophobic material (e.g., the layer of the hydrophobic material) may be at least partially porous. According to some embodiments, for example, the hydrophobic material comprises a plurality of pores. The plurality of pores of the hydrophobic material may have any of a variety of suitable average characteristic dimensions (e.g., average diameters). In certain embodiments, for example, the plurality of pores of the hydrophobic material have an average characteristic dimension greater than or equal to 0.01 micrometers, greater than or equal to 0.05 micrometers, greater than or equal to 0.1 micrometers, greater than or equal to 0.5 micrometers, greater than or equal to 1 micrometer, greater than or equal to 2 micrometers, greater than or equal to 3 micrometers, greater than or equal to 4 micrometers, greater than or equal to 5 micrometers, greater than or equal to 6 micrometers, greater than or equal to 7 micrometers, greater than or equal to 8 micrometers, or greater than or equal to 9 micrometers. In some embodiments, the plurality of pores of the hydrophobic material have an average characteristic dimension less than or equal to 10 micrometers, less than or equal to 9 micrometers, less than or equal to 8 micrometers, less than or equal to 7 micrometers, less than or equal to 6 micrometers, less than or equal to 5 micrometers, less than or equal to 4 micrometers, less than or equal to 3 micrometers, less than or equal to 2 micrometers, less than or equal to 1 micrometer, less than or equal to 0.5 micrometers, less than or equal to 0.1 micrometers, or less than or equal to 0.05 micrometers. Combinations of the above recited ranges are possible (e.g., the plurality of pores of the hydrophobic material have an average characteristic dimension greater than or equal to 0.01 micrometers and less than or equal to 10 micrometers, the plurality of pores of the hydrophobic material have an average characteristic dimension greater than or equal to 3 micrometers and less than or equal to 4 micrometers). Other ranges are also possible. In some embodiments, the average characteristic dimension (e.g., average diameter) of the plurality of pores of the hydrophobic material may be determined by SEM.

[0063] In some embodiments, the hydrophobic material (e.g., the layer of the hydrophobic material) is a gas diffusion layer (e.g., a hydrophobic gas diffusion layer). In certain embodiments, for example, the gas diffusion layer comprises a plurality of pores that are configured to provide a pathway for transport (e.g., diffusion) of a gas from the second surface of the gas diffusion layer to the first surface of the gas diffusion layer that is substantially opposite the second surface. Referring, for example, to FIG. 1 A, the layer of hydrophobic material 102 (e.g., the gas diffusion layer) may comprise a plurality of pores configured to provide a pathway for transport of a gas from second surface 110a of the layer of hydrophobic material 102 to first surface 108a of the layer of hydrophobic material 102 that is substantially opposite second surface 110a.

[0064] In certain embodiments, the layer of the hydrophobic material (e.g., the gas diffusion layer) is configured to provide a substantial barrier to transport of water or an aqueous solution from the first surface of the gas diffusion layer to the second surface of the gas diffusion layer that is substantially opposite the first surface. Referring, for example, to FIG. 1 A, the layer of hydrophobic material 102 is configured to provide a substantial barrier to transport of water or an aqueous solution from first surface 108a of the layer of hydrophobic material 102 to second surface 110a of the layer of hydrophobic material 102 that is substantially opposite first surface 108a.

[0065] The hydrophobic material may comprise any of a variety of suitable materials. In certain embodiments, the hydrophobic material comprises an electrically insulating material. In some embodiments, the hydrophobic material comprises one or more polymers. According to certain embodiments, suitable polymers include, but are not limited to, polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), and / or combinations thereof. Other polymers and / or materials are also possible.

[0066] According to certain embodiments, the hydrophobic material may comprise a mixture of materials. For example, in some embodiments, the hydrophobic material comprises a comparatively less hydrophobic material coated with a comparatively more hydrophobic material. In certain embodiments, the hydrophobic material comprises a mixture of hydrophobic materials.

[0067] According to certain embodiments, the composite article comprises a catalyst material. Referring, for example, to FIGS. 1A-1B, composite article 100a comprises catalyst material 104.

[0068] In some embodiments, the catalyst material is configured as a layer. For example, as shown in FIGS. 1 A-1B, catalyst material 104 is configured a layer. In certain embodiments, the layer of the catalyst material comprises a first surface and a second surface that is substantially opposite the first surface. Referring to FIG. 1 A, for example, the layer of catalyst material 104 comprises first surface 108b and second surface 110b that is substantially opposite first surface 108b.

[0069] The layer of the catalyst material may have any of a variety of suitable thicknesses. For example, referring to FIG. 1A, the layer of catalyst material 104 has thickness 112b. In some embodiments, the layer of the catalyst material has a thickness greater than or equal to 1 nanometer, greater than or equal to 5 nanometers, greater than or equal to 10 nanometers, greater than or equal to 50 nanometers, greater than or equal to 100 nanometers, greater than or equal to 500 nanometers, greater than or equal to 1 micrometer, greater than or equal to 5 micrometers, greater than or equal to 10 micrometers, or greater than or equal to 15 micrometers. In certain embodiments, the layer of the catalyst material has a thickness less than or equal to 20 micrometers, less than or equal to 15 micrometers, less than or equal to 10 micrometers, less than or equal to 5 micrometers, less than or equal to 1 micrometer, less than or equal to 500 nanometers, less than or equal to 100 nanometers, less than or equal to 50 nanometers, less than or equal to 10 nanometers, or less than or equal to 5 nanometers. Combinations of the above recited ranges are possible (e.g., the layer of the catalyst material has a thickness greater than or equal to 1 nanometer and less than or equal to 20 micrometers, the layer of the catalyst material has a thickness greater than or equal to 100 nanometers and less than or equal to 500 nanometers). Other ranges are also possible. In some embodiments, the thickness of the layer of the catalyst material is determined by SEM.

[0070] While the layer of catalyst material 104 is depicted in FIG. 1 A as a smooth layer of uniform thickness, those of ordinary skill in the art would understand that this is for illustration purposes only and the thickness of the layer of the catalyst material may have a particular roughness and / or may vary in thickness, in accordance with some embodiments. In certain embodiments, the layer of the catalyst material may be of relatively uniform thickness (e.g., within less than or equal to 10% of the total thickness) over at least a substantial portion of the layer of the catalyst material (e.g., greater than or equal to 75% of the surface area of the layer of the catalyst material).

[0071] According to certain embodiments, the catalyst material (e.g., the layer of the catalyst material) may be at least partially porous. In some embodiments, for example, the catalyst material comprises a plurality of pores. The plurality of pores may have any of a variety of suitable average characteristic dimensions (e.g., average diameters). In certain embodiments, for example, the plurality of pores of the catalyst material have an average characteristic dimension greater than or equal to 0.1 nanometers, greater than or equal to 0.5 nanometers, greater than or equal to 1 nanometer, greater than or equal to 5 nanometers, greater than or equal to 10 nanometers, greater than or equal to 50 nanometers, greater than or equal to 100 nanometers, greater than or equal to 500 nanometers, greater than or equal to 1 micrometer, or greater than or equal to 5 micrometers. In some embodiments, the plurality of the pores of the catalyst material have an average characteristic dimension less than or equal to 10 micrometers, less than or equal to 5 micrometers, less than or equal to 1 micrometer, less than or equal to 500 nanometers, less than or equal to 100 nanometers, less than or equal to 50 nanometers, less than or equal to 10 nanometers, less than or equal to 5 nanometers, less than or equal to 1 nanometer, or less than or equal to 0.5 nanometers. Combinations of the above recited ranges are possible (e.g., the plurality of pores of the catalyst material have an average characteristic dimension greater than or equal to 0.1 nanometers and less than or equal to 10 micrometers, the plurality of pores of the catalyst material have an average characteristic dimension greater than or equal to 50 nanometers and less than or equal to 100 nanometers). Other ranges are also possible. In some embodiments, the average characteristic dimensions (e.g., average diameter) of the plurality of pores of the catalyst material may be determined by SEM.

[0072] In certain embodiments, the catalyst material may adopt the same or substantially the same porosity as the hydrophobic material. For example, in certain embodiments wherein the catalyst material is deposited on the hydrophobic material (as explained herein in greater detail), the average characteristic dimension of the plurality of pores of the catalyst material may be the same or substantially the same as the average characteristic dimension of the plurality of pores of the catalyst material. According to some embodiments, the average characteristic dimension of the plurality of pores of the catalyst material may be within less than or equal to 20%, less than or equal to 10%, less than or equal to 5%, or less than or equal to 1% of the average characteristic dimension of the plurality of pores of the hydrophobic material.

[0073] In some embodiments, the composite article may be configured such that the layer of the hydrophobic material (e.g., the gas diffusion layer) is a support for the layer of the catalyst material. In certain embodiments, for example, the layer of the hydrophobic material is disposed on the second surface of the layer of the catalyst material. Referring to FIG. 1 A, for example, composite article 100a is configured such that the layer of hydrophobic material 102 is disposed on second surface 110b of the layer of catalyst material 104. In certain embodiments, first surface 108a of the layer of hydrophobic material 102 and second surface According to certain embodiments, the catalyst material may be configured to catalyze a conversion of one or more gases. In some embodiments, the catalyst material may be configured to catalyze a reduction of one or more gases. For example, in certain embodiments, the catalyst material is configured to be oxidized (e.g., upon the application of a potential) such that the catalyst material provides one or more electrons to reduce the one or more gases.

[0074] The catalyst material may comprise any of a variety of suitable materials. In some embodiments, the catalyst material comprises a metal. According to certain embodiments, suitable metals include, but are not limited to, copper (Cu), silver (Ag), gold (Au), zinc (Zn), and / or combinations thereof. Other metals and / or materials are also possible.

[0075] According to certain embodiments, the composite article comprises an electrically conductive material. Referring, for example, to FIGS. 1 A-1B, composite article 100a comprises electrically conductive material 106 (e.g., 106a, 106b, 106c, and 106d). Electrically conductive material 106 is represented as a dashed line in the cross-section shown in FIG. 1 A, and as a dot in the top-view shown in FIG. IB.

[0076] The electrically conductive material may have any of a variety of suitable electrical conductivities. In some embodiments, for example, the electrically conductive material has an electrical conductivity greater than or equal to 104S / m, greater than or equal to 105S / m, greater than or equal to 106S / m, or greater than or equal to 107S / m. In some embodiments, the electrically conductive material has an electrical conductivity less than or equal to 108S / m, less than or equal to 107S / m, less than or equal to 106S / m, or less than or equal to 105S / m. Combinations of the above recited ranges are possible (e.g., the electrically conductive material has an electrical conductivity greater than or equal to 104S / m and less than or equal to 108S / m, the electrically conductive material has an electrical conductivity greater than or equal to 105S / m and less than or equal to 107S / m). Other ranges are also possible. In some embodiments, the electrical conductivity of the electrically conductive material may be determined by a four-point probe.

[0077] The electrically conductive material may have any of a variety of suitable configurations. In some embodiments, for example, at least a portion of the electrically conductive material is configured as a post, a pillar, a wire, a column, a tube, and / or the like.

[0078] According to certain embodiments, the electrically conductive material is configured to provide an electrically conductive pathway. In some embodiments, the electrically conductive pathway provided by the electrically conductive material may, in some embodiments, be an electrically conductive pathway from a source of electrons to the first surface of the layer of the catalyst material. The source of electrons may, in some embodiments, be a current collector, as explained herein in greater detail.

[0079] In some embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer). Referring to FIG. 1 A, for example, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a and 106b) from the source of electrons (not shown in FIG. 1A) to first surface 108b of the layer of catalyst material 104 travels through thickness 112a of the layer of hydrophobic material 102. In some embodiments, at least a portion of the electrically conductive material pierces through the first surface and / or the second surface of the layer of the hydrophobic material. Referring, for example, to FIG. 1 A, at least a portion of electrically conductive material 106 (e.g., 106a and 106b) pierces through first surface 110a and / or second surface 108a of the layer of hydrophobic material 102.

[0080] In certain embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the catalyst material. Referring to FIG. 1 A, for example, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a and 106b) from the source of electrons (not shown in FIG. 1A) to first surface 108b of the layer of catalyst material 104 travels through thickness 112b of the layer of catalyst material 104. In some embodiments, at least a portion of the electrically conductive material pierces through the first surface and / or the second surface of the layer of the catalyst material. For example, referring to FIG. 1 A, at least a portion of electrically conductive material 106 (e.g., 106a and 106b) pierces through first surface 108b and / or second surface 110b of the layer of catalyst material 104.

[0081] In some embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer) and through the thickness of the layer of the catalyst material. For example, as shown in FIG. 1 A, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a and 106b) from the source of electrons (not shown in FIG. 1A) to first surface 108b of the layer of catalyst material 104 travels through thickness 112a of the layer of the hydrophobic material 102 and through thickness 112b of the layer of catalyst material 104. In some embodiments, at least a portion of the electrically conductive material pierces through the first surface and / or the second surface of the layer of the hydrophobic material and through the first surface and / or the seconds surface of the layer of the catalyst material. Referring to FIG. 1 A, for example, at least a portion of electrically conductive material 106 (e.g., 106a and 106b) pierces through first surface 108a and / or second surface 110a of the layer of hydrophobic material 102 and through first surface 108b and / or second surface 110b of the layer of catalyst material 104.

[0082] In some embodiments at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels along the first surface of the layer of the catalyst material. FIG. 2A shows, according to some embodiments, a cross-sectional schematic diagram of composite article 100b. FIG. 2B shows, according to some embodiments, a top-view schematic diagram of composite article 100b. The cross-section shown in FIG. 2A is taken along dotted line 2A in FIG. 2B. Electrically conductive material 106 (e.g., 106a, 106b, 106c, and 106d) is represented as a dashed line in the cross-section shown in FIG. 2A and in the top-view shown in FIG. 2B. Referring to FIGS. 2A-2B, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a, 106b, 106c, and 106d) from the source of electrons (not shown in FIGS. 2A- 2B) to first surface 108b of the layer of catalyst material 104 travels along first surface 108b of the layer of catalyst material 104. In certain embodiments, at least a portion of the electrically conductive material is in direct contact with the first surface of the layer of the catalyst material. For example, as shown in FIG. 2 A, at least a portion of electrically conductive material 106 (e.g., 106a and 106b) is in direct contact with first surface 108b of the layer of catalyst material 104.

[0083] According to certain embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer), through the thickness of the layer of the catalyst material, and along the first surface of the layer of the catalyst material. For example, as shown in FIG. 2A, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a and 106b) from the source of electrons (not shown in FIG. 2 A) to first surface 108b of the layer of catalyst material 104 travels through thickness 112a of the layer of hydrophobic material 102, through thickness 112b of the layer of catalyst material 104, and along first surface 108b of the layer of catalyst material 104. In some embodiments, at least a portion of the electrically conductive material pierces through the first surface and / or the second surface of the layer of the hydrophobic material, through the first surface and / or the second surface of the layer of the catalyst material, and is in direct contact with the first surface of the layer of the catalyst material. For example, as shown in FIG. 2 A, at least a portion of electrically conductive material 106 pierces through fist surface 108a and / or second surface 110a of the layer of hydrophobic material 102, through first surface 108b and / or second surface 110b of the layer of catalyst material 104, and is in direct contact with first surface 108b of the layer of catalyst material 104.

[0084] According to some embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material does not travel through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer). FIG. 3A shows, according to some embodiments, a cross-sectional schematic diagram of composite article 100c. FIG. 3B shows, according to some embodiments, a top-view schematic diagram of composite article 100c. The cross-section shown in FIG. 3A is taken along dotted line 3A in FIG. 3B. Electrically conductive material 106 (e.g., 106a and 106b) is represented as a dashed line in the cross-section shown in FIG. 3A and in the top-view shown in FIG. 3B. Referring to FIG. 3 A, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a) from the source of electrons (not shown in FIG. 3A) to first surface 108b of the layer of catalyst material 104 does not travel through thickness 112a of the layer of hydrophobic material 102.

[0085] In certain embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material does not travel through the thickness of the layer of the catalyst material. Referring to FIG. 3 A, for example, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a) from the source of electrons (not shown in FIG. 3 A) to first surface 108b of the layer of catalyst material 104 does not travel through thickness 112b of the layer of catalyst material 104.

[0086] In some embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels along the first surface of the layer of the catalyst material but does not travel through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer) or through the thickness of the layer of the catalyst material. For example, as shown in FIG. 3A, at least a portion of the electrically conductive pathway provided by electrically conductive material 106 (e.g., 106a) from the source of electrons (not shown in FIG. 3 A) to first surface 108b of the layer of catalyst material 104 travels along first surface 108b of the layer of catalyst material 104 but does not travel through thickness 112a of the layer of hydrophobic material 102 or through thickness 112b of the layer of catalyst material 104.

[0087] Other configurations for the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material not shown in FIGS. 1 A-3B are also possible, as would be recognizable by a person of ordinary skill in the art. In certain embodiments, for example, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the catalyst material travels through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer) and along the first surface of the layer of the catalyst material but does not travel through the thickness of the layer of the catalyst material.

[0088] In some embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the catalyst material but does not travel through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer).

[0089] In certain embodiments, at least a portion of the electrically conductive pathway provided by the electrically conductive material from the source of electrons to the first surface of the layer of the catalyst material travels through the thickness of the layer of the catalyst material and along the first surface of the layer of the catalyst material but does not travel through the thickness of the layer of the hydrophobic material (e.g., the gas diffusion layer).

[0090] According to certain embodiments, the electrically conductive material may occupy a small amount of the surface area of the catalyst material. In some embodiments, the electrically conductive material advantageously decreases the active surface area of the catalyst material by a negligible amount. Referring to FIGS. IB, 2B, and 3B, for example, electrically conductive material 106 occupies an advantageously small amount of the surface area of first surface 108b of the layer of catalyst material 104. In certain embodiments, the electrically conductive material occupies less than or equal to 5%, less than or equal to 4.5%, less than or equal to 4%, less than or equal to 3.5%, less than or equal to 3%, less than or equal to 2.5%, less than or equal to 2%, or less than or equal to 1.5% of the surface area of the catalyst material. In some embodiments, the electrically conductive material occupies greater than or equal to 1%, greater than or equal to 1.5%, greater than or equal to 2%, greater than or equal to 2.5%, greater than or equal to 3%, greater than or equal to 3.5%, greater than or equal to 4%, or greater than or equal to 4.5% of the surface area of catalyst material. Combinations of the above recited ranges are also possible (e.g., the electrically conductive material occupies less than or equal to 5% and greater than or equal to 1% of the surface area of the catalyst material, the electrically conductive material occupies less than or equal to 3.5% and greater than or equal to 2.5% of the surface area of the catalyst material). Other ranges are also possible.

[0091] According to some embodiments, the composite article may comprise a plurality of electrically conductive materials. Referring to FIGS. IB and 2B, for example, composite articles 100a and 100b, respectively, comprise electrically conductive materials 106a, 106b, 106c, and 106d. Referring to FIG. 3B, composite article 100c comprises electrically conductive materials 106a and 106b. Although four electrically conductive materials are shown in FIGS. IB and 2B and two electrically conductive materials are shown in FIGS. 3B, more electrically conductive materials are possible (e.g., the composite article may comprise three electrically conductive materials, four electrically conductive materials, five electrically conductive materials, ten electrically conductive materials, twenty electrically conductive materials, fifty electrically conductive materials, one hundred electrically conductive materials, etc.).

[0092] According to some embodiments, the plurality of electrically conductive materials may be discontinuous. In certain embodiments, for example, each electrically conductive material in the plurality of electrically conductive materials may have a characteristic spacing from a neighboring electrically conductive material in the plurality of electrically conductive materials. Referring, for example, to FIGS. IB and 2B, electrically conductive materials 106a, 106b, 106c, and 106d are discontinuous. In certain embodiments, electrically conductive material 106a has characteristic spacing 118a from electrically conductive material 106c. In some embodiments, electrically conductive material 106c has characteristic spacing 118b from electrically conductive material 106d. In FIGS. IB and 2B, the characteristic spacing between electrically conductive material 106a and 106b and the characteristic spacing between electrically conductive material 106b and 106d are not shown for clarity. Referring to FIG. 3B, electrically conductive materials 106a and 106b are discontinuous. In certain embodiments, electrically conductive material 106a has characteristic spacing 118a from electrically conductive material 106b.

[0093] The average characteristic spacing between neighboring electrically conductive materials may be any of a variety of suitable values. In certain embodiments, for example, the average characteristic spacing between neighoring electrically conductive materials is greater than or equal to 0.1 millimeter, greater than or equal to 0.5 millimeters, greater than or equal to 1 millimeter, greater than or equal to 5 millimeters, greater than or equal to 10 millimeters, greater than or equal to 20 millimeters, greater than or equal to 30 millimeters, greater than or equal to 40 millimeters, greater than or equal to 50 millimeters, greater than or equal to 60 millimeters, greater than or equal to 70 millimeters, greater than or equal to 80 millimeters, or greater than or equal to 90 millimeters. In some embodiments, the average characteristic spacing between neighboring electrically conductive materials is less than or equal to 100 millimeters, less than or equal to 90 millimeters, less than or equal to 80 millimeters, less than or equal to 70 millimeters, less than or equal to 60 millimeters, less than or equal to 50 millimeters, less than or equal to 40 millimeters, less than or equal to 30 millimeters, less than or equal to 20 millimeters, less than or equal to 10 millimeters, less than or equal to 5 millimeters, less than or equal to 1 millimeter, or less than or equal to 0.5 millimeter. Combinations of the above recited ranges are possible (e.g., the average characteristic spacing between neighboring electrically conductive materials is greater than or equal to 0.1 millimeter and less than or equal to 100 millimeters, the average characteristic spacing between neighboring electrically conductive materials is greater than or equal to 5 millimeters and less than or equal to 10 millimeters). Other ranges are also possible.

[0094] According to some embodiments, the characteristic spacing between neighboring electrically conductive materials may depend on the average characteristic dimension (e.g., average diameter) of the electrically conductive material. For example, in certain embodiments wherein larger sized electrically conductive materials are used, the characteristic spacing between neighboring electrically conductive materials may be increased. In other embodiments wherein smaller sized electrically conductive materials are used, the characteristic spacing between neighboring electrically conductive materials may be decreased.

[0095] The average characteristic dimension (e.g., average diameter) of the electrically conductive material may be any of a variety of suitable values. In certain embodiments, for example, the average characteristic dimension of the electrically conductive material is greater than or equal to 10 micrometers, greater than or equal to 25 micrometers, greater than or equal to 50 micrometers, greater than or equal to 100 micrometers, greater than or equal to 250 micrometers, greater than or equal to 500 micrometers, greater than or equal to 750 micrometers, greater than or equal to 1 millimeter, greater than or equal to 2 millimeters, greater than or equal to 3 millimeters, or greater than or equal to 4 millimeters. In some embodiments, the average characteristic dimension of the electrically conductive material is less than or equal to 5 millimeters, less than or equal to 4 millimeters, less than or equal to 3 millimeters, less than or equal to 2 millimeters, less than or equal to 1 millimeter, less than or equal to 750 micrometers, less than or equal to 500 micrometers, less than or equal to 250 micrometers, less than or equal to 100 micrometers, less than or equal to 50 micrometers, or less than or equal to 25 micrometers. Combinations of the above recited ranges are possible (e.g., the average characteristic dimension of the electrically conductive material is greater than or equal to 10 micrometers and less than or equal to 5 millimeters, the average characteristic dimension of the electrically conductive material is greater than or equal to 500 micrometers and less than or equal to 750 micrometers). Other ranges are also possible.

[0096] The electrically conductive material may comprise any of a variety of suitable materials. In some embodiments, for example, the electrically conductive material comprises a metal. According to certain embodiments, suitable metals include, but are not limited to, Cu, Ag, and / or combinations thereof. Other materials are also possible.

[0097] In some embodiments, the electrically conductive material and the catalyst material comprise the same material. In other embodiments, the electrically conductive material and the catalyst material comprise a different material.

[0098] The composite articles described herein may be fabricated according to methods known to a person of ordinary skill in the art. In certain embodiments, for example, the catalyst material is deposited on the hydrophobic material. The deposition of the catalyst material on the hydrophobic material may be via any of a variety of suitable methods, including, for example, sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), and / or the like. In some embodiments, the electrically conductive material is added to the hydrophobic material / catalyst material composite structure by forming one or more holes through the hydrophobic material / catalyst material composite structure and passing the electrically conductive material through the one or more holes. In certain embodiments, the one or more holes in the hydrophobic material / catalyst material composite structure may be formed by punching. In some embodiments, the electrically conductive material may be passed through the one or more holes using a needle and thread. According to certain embodiments, the composite article may be an electrode (e.g., a gas diffusion electrode). In some embodiments, the electrode is a catalytic, aqueous barrier, gas diffusion electrode.

[0099] In some embodiments, at least a portion of the electrode is configured to provide a pathway for transport of a gas. As explained herein in greater detail, for example, the electrode may comprise a gas diffusion layer comprising a plurality of pores that are configured to provide a pathway for transport (e.g., diffusion) of a gas from a second surface of the gas diffusion layer to a first surface of the gas diffusion layer that is substantially opposite the second surface. Referring to FIGS. 1A, 2A, and 3A, for example, the composite article (e.g., the electrodes), e.g., composite articles 100a, 100b, and 100c, respectively, comprise a layer of hydrophobic material 102 (e.g., a gas diffusion layer) comprising a plurality of pores that are configured to provide a pathway for transport of a gas from second surface 110a of the layer of hydrophobic material 102 to first surface 108a of the layer of hydrophobic material 102 that is substantially opposite second surface 110a.

[0100] The electrode may have any of a variety of suitable gas permeabilities across at least a portion of the electrode. According to certain embodiments, the gas permeability of the electrode across at least a portion of the electrode is the volumetric gas flow rate over a unit area of the gas diffusion layer at a specific pressure difference across the gas diffusion layer. In some embodiments, for example, the electrode has a gas permeability across at least a portion of the electrode of at least 0.05 ft3 / min ft2at 125 Pa, at least 0.1 ft3 / min ft2at 125 Pa, at least 0.5 ft3 / min ft2at 125 Pa, at least 1 ft3 / min ft2at 125 Pa, at least 2 ft3 / min ft2at 125 Pa, at least 3 ft3 / min ft2at 125 Pa, at least 4 ft3 / min ft2at 125 Pa, at least 5 ft3 / min ft2at 125 Pa, at least 6 ft3 / min ft2at 125 Pa, or at least 7 ft3 / min ft2at 125 Pa. In certain embodiments, the electrode has a gas permeability across at least a portion of the electrode of less than or equal to 8 ft3 / min ft2at 125 Pa, less than or equal to 7 ft3 / min ft2at 125 Pa, less than or equal to 6 ft3 / min ft2at 125 Pa, less than or equal to 5 ft3 / min ft2at 125 Pa, less than or equal to 4 ft3 / min ft2at 125 Pa, less than or equal to 3 f / min ft2at 125 Pa, less than or equal to 2 ft3 / min ft2at 125 Pa, less than or equal to 1 f / min ft2at 125 Pa, less than or equal to 0.5 ft3 / min ft2at 125 Pa, or less than or equal to 0.1 ft3 / min ft2at 125 Pa. Combinations of the above recited ranges are possible (e.g., the electrode has a gas permeability across at least a portion of the electrode of at least 0.05 ft3 / min ft2at 125 Pa and less than or equal to 8 ft3 / min ft2at 125 Pa, the electrode has a gas permeability across at least a portion of the electrode of at least 2 ft3 / min ft2at 125 Pa and less than or equal to 3 ft3 / min ft2at 125 Pa). Other ranges are also possible. According to some embodiments, the gas permeability of the electrode across at least a portion of the electrode is determined by measuring the rate of gas flow through a known area of the electrode by applying a pressure differential across the area of the electrode.

[0101] In certain embodiments, at least a portion of the electrode is configured to provide a substantial barrier to transport of an electrolyte. In certain embodiments, the electrolyte may be a liquid electrolyte comprising, for example, water or an aqueous solution. As explained herein in greater detail, for example, the electrode may comprise a gas diffusion layer that is configured to provide a substantial barrier to transport of an electrolyte across the electrode from a first surface of the electrode to a second surface of the electrode, wherein the second surface of the electrode is substantially opposite the first surface. Referring, for example, to FIGS. 1 A, 2A, and 3A, the composite article (e.g., the electrodes), e.g., composite articles 100a, 100b, and 100c, respectively, comprise a layer of hydrophobic material 102 (e.g., a gas diffusion layer) configured to provide a substantial barrier to transport of an electrolyte across the composite article from a first surface of the composite article (e.g., first surface 108b of the layer of catalyst material 104) to a second surface of the composite article (e.g., second surface 110a of the layer of hydrophobic material 102).

[0102] The electrode may have any of a variety of suitable water permeabilities across at least a portion of the electrode. According to some embodiments, the water permeability across at least a portion of the electrode is measured as the water entry (or breakthrough) pressure, which is the pressure differential required to force water into the gas diffusion layer. In certain embodiments, for example, the electrode has a water entry pressure of less than or equal to 100 psi, less than or equal to 90 psi, less than or equal to 80 psi, less than or equal to 70 psi, less than or equal to 60 psi, less than or equal to 50 psi, less than or equal to 40 psi, less than or equal to 30 psi, less than or equal to 20 psi, less than or equal to 10 psi, less than or equal to 5 psi, less than or equal to 1 psi, less than or equal to 0.5 psi, or less than or equal to 0.1 psi across at least a portion of the electrode. In some embodiments, the electrode has a water entry pressure of greater than or equal to 0.05 psi, greater than or equal to 0.1 psi, greater than or equal to 0.5 psi, greater than or equal to 1 psi, greater than or equal to 5 psi, greater than or equal to 10 psi, greater than or equal to 20 psi, greater than or equal to 30 psi, greater than or equal to 40 psi, greater than or equal to 50 psi, greater than or equal to 60 psi, greater than or equal to 70 psi, greater than or equal to 80 psi, or greater than or equal to 90 psi across at least a portion of the electrode. Combinations of the above recited range are possible (e.g., the electrode has a water entry pressure of less than or equal to 100 psi and greater than or equal to 0.05 psi across at least a portion of the electrode, the electrode has a water entry pressure of less than or equal to 40 psi and greater than or equal to 30 psi across at least a portion of the electrode). Other ranges are also possible. According to some embodiments, the water entry pressure of the electrode across at least a portion of the electrode is determined by measuring the pressure differential required to force water into the gas diffusion layer.

[0103] In certain embodiments wherein an electrolyte (e.g., water or an aqueous solution) leaks through one or more holes in the layer of the catalyst material and / or the layer of the hydrophobic material formed by the electrically conductive material, the hydrophobicity of the hydrophobic material prevents substantial flooding of the gas diffusion layer that is commonly observed in conventional carbon paper gas diffusion layers.

[0104] According to certain embodiments, at least a portion of the electrode is configured to be exposed to an electrolyte (e.g., water or an aqueous solution). For example, as explained herein in greater detail, the electrode may comprise a layer of a catalyst material that is configured to be exposed to an electrolyte in contact with a first surface of the electrode. Referring, for example, to FIGS. 1 A, 2A, and 3A, the composite article (e.g., the electrodes), e.g., composite articles 100a, 100b, and 100c, respectively, comprise a layer of catalyst material 104 configured to be exposed to an electrolyte in contact with a first surface of the composite article (e.g., first surface 108b of the layer of catalyst material 104).

[0105] In some embodiments, at least a portion of the electrode is configured to be in electrical communication with a source of electrons (e.g., a current collector). For example, as explained herein in greater detail, the electrode may comprise an electrically conductive material that is configured to be in electrical communication with a current collector such that the electrically conductive material provides an electrically conductive pathway from the current collector to the first surface of the layer of the catalyst material. For example, referring to FIGS. 1 A, 2A, and 3A, the composite article (e.g., the electrodes), e.g., composite articles 100a, 100b, and 100c, respectively, comprise electrically conductive material 106 configured to be in electrical communication with a current collector (not shown in FIGS. 1A, 2A, and 3A) such that electrically conductive material 106 provides an electrically conductive pathway from the current collector to first surface 108b of the layer of catalyst material 104.

[0106] In certain embodiments, at least a portion of the electrode is configured to provide electronic conductivity to at least some of the catalyst material. As explained in greater detail herein, for example, the electrode may comprise an electrically conductive material that is configured to provide electronic conductivity to at least some of the catalyst material. For example, referring to FIGS. 1 A, 2A, and 3A, the composite article (e.g., the electrodes), e.g., composite articles 100a, 100b, and 100c, respectively, comprise electrically conductive material 106 that is configured to provide electronic conductivity to at least some of the layer of catalyst material 104.

[0107] According to certain embodiments, and as explained herein in greater detail, the catalyst material may be configured to be exposed to the electrolyte in contact with the first surface of the electrode. In some embodiments, the catalyst material is configured to be in contact with a gas in the electrolyte. In certain embodiments, by providing electronic conductivity to at least some of the catalyst material, the catalyst material may be configured to convert (e.g., reduce) the gas at the interface between the catalyst material, the electrolyte, and the gas.

[0108] The composite article (e.g., electrode) may have any of a variety of suitable geometric areas. Referring, for example, to FIGS. IB, 2B, and 3B, the composite articles (e.g., composite articles 100a, 100b, and 100c, respectively) have a geometric area equal to length 114 times width 116. According to some embodiments, the composite article has a geometric area greater than or equal to 5 cm2, greater than or equal to 10 cm2, greater than or equal to 20 cm2, greater than or equal to 30 cm2, greater than or equal to 40 cm2, greater than or equal to 50 cm2, greater than or equal to 60 cm2, greater than or equal to 70 cm2, greater than or equal to 80 cm2, greater than or equal to 90 cm2, greater than or equal to 100 cm2, greater than or equal to 200 cm2, greater than or equal to 300 cm2, greater than or equal to 400 cm2, greater than or equal to 500 cm2, greater than or equal to 600 cm2, greater than or equal to 700 cm2, greater than or equal to 800 cm2, greater than or equal to 900 cm2, greater than or equal to 1,000 cm2, greater than or equal to 2,000 cm2, greater than or equal to 3,000 cm2, greater than or equal to 4,000 cm2, greater than or equal to 5,000 cm2, greater than or equal to 6,000 cm2, greater than or equal to 7,000 cm2, greater than or equal to 8,000 cm2, or greater than or equal to 9,000 cm2. In some embodiments, the composite article has a geometric area less than or equal to 10,000 cm2, less than or equal to 9,000 cm2, less than or equal to 8,000 cm2, less than or equal to 7,000 cm2, less than or equal to 6,000 cm2, less than or equal to 5,000 cm2, less than or equal to 4,000 cm2, less than or equal to 3,000 cm2, less than or equal to 2,000 cm2, less than or equal to 1,000 cm2, less than or equal to 900 cm2, less than or equal to 800 cm2, less than or equal to 700 cm2, less than or equal to 600 cm2, less than or equal to 500 cm2, less than or equal to 400 cm2, less than or equal to 300 cm2, less than or equal to 200 cm2, less than or equal to 100 cm2, less than or equal to 90 cm2, less than or equal to 80 cm2, less than or equal to 70 cm2, less than or equal to 60 cm2, less than or equal to 50 cm2, less than or equal to 40 cm2, less than or equal to 30 cm2, less than or equal to 20 cm2, less than or equal to 10 cm2, or less than or equal to 5 cm2. Combinations of the above recited ranges are possible (e.g., the composite article has a geometric area greater than or equal to 1 cm2and less than or equal to 10,000 cm2, the composite article has a geometric area greater than or equal to 100 cm2and less than or equal to 200 cm2). Other ranges are also possible.

[0109] According to certain embodiments, a method of electrochemically converting a gas to one or more products is described. In some embodiments, the method comprises providing an electrochemical cell comprising a composite article (e.g., an electrode) as described herein. FIGS. 4A-4C show, according to some embodiments, cross-sectional schematic diagrams of electrochemical cells (e.g., electrochemical cells 400a, 400b, and 400c, respectively) comprising a composite article (e.g., composite articles 100a, 100b, and 100c, respectively). Referring to FIGS. 5A-5C, composite articles 100a, 100b, and 100c may be electrodes, in some embodiments, as described herein in further detail.

[0110] The electrochemical cell may comprise a first current collector, a membrane (or separator), a second electrode, and a second current collector. As shown in FIGS. 4A-4C, for example, the electrochemical cells (e.g., electrochemical cells 400a, 400b, and 400c, respectively) comprise first current collector 402, membrane 404 (or separator), second electrode 406, and second current collector 408.

[0111] According to some embodiments, the first current collector is disposed on the second surface of the layer of the hydrophobic material. Referring to FIGS. 4A-4C, for example, first current collector 402 is disposed on second surface 110a of the layer of hydrophobic material 102. In some embodiments, the first current collector and the second surface of the layer of the hydrophobic material are in direct contact. For example, as shown in FIGS. 4A- 4C, first current collector 502 and second surface 110a of the layer of hydrophobic material 102 are in direct contact.

[0112] In certain embodiments, as described herein in greater detail, the electrically conductive material of the composite article is configured to provide an electrically conductive pathway from a source of electrons (e.g., a current collector) to the first surface of the layer of the catalyst material. For example, referring to FIGS. 4A-4C, electrically conductive material 106 of the composite articles (e.g., composite articles 100a, 100b, and 100c, respectively) is configured to provide an electrically conductive pathway from first current collector 402 to first surface 108b of the layer of catalyst material 104. According to some embodiments, at least a portion of the electrically conductive material is in direct contact with the first current collector. Referring to FIGS. 4A-4C, for example, at least a portion of electrically conductive material 106 is in direct contact with first current collector 402. In certain embodiments, at least a portion of the electrically conductive material is in direct contact with the first surface of the layer of the catalyst material. For example, referring to FIGS. 4A-4C, at least a portion of electrically conductive material 106 is in direct contact with first surface 108b of the layer of catalyst material 104.

[0113] The first current collector may comprise any of a variety of suitable materials. In some embodiments, for example, the first current collector comprises a carbon-containing material (e.g., graphene, graphite, etc.). Other materials are also possible and would be known to a person of ordinary skill in the art.

[0114] In certain embodiments, the membrane (or separator) is disposed on the first surface of the layer of the catalyst material. Referring, for example, to FIGS. 4A-4C, membrane 404 (or separator) is disposed on first surface 108b of the layer of catalyst material 104.

[0115] The membrane (or separator) may comprise any of a variety of suitable materials. According to certain embodiments, the membrane (or separator) is semipermeable. In some embodiments, for example, the membrane (or separator) is an anion exchange membrane comprising a polymer. Other materials are also possible and would be known to a person of ordinary skill in the art.

[0116] According to some embodiments, the second electrode is disposed on the membrane. For example, referring to FIGS. 4A-4C, second electrode 406 is disposed on membrane 404.

[0117] The second electrode may comprise any of a variety of suitable materials. In certain embodiments, for example, the second electrode comprises a metal and / or a metal oxide (e.g., iridium oxide). Other materials are also possible and would be known to a person of ordinary skill in the art.

[0118] In some embodiments, the second current collector is disposed on the second electrode. Referring, for example, to FIGS. 4A-4C, second current collector 408 is disposed on second electrode 406.

[0119] The second current collector may comprise any of a variety of suitable materials. In certain embodiments, for example, the second current collector comprises a metal (e.g., titanium). Other materials are also possible and would be known to a person of ordinary skill in the art.

[0120] In certain embodiments, the electrochemical cell may comprise an electrolyte (not shown in FIGS. 4A-4C). According to some embodiments, the electrolyte is configured to be in direct contact with the first surface of the layer of the catalyst material. Referring to FIGS. 4A-4C, for example, the electrolyte is configured to be in direct contact with first surface 108b of the layer of catalyst material 104. According to certain embodiments, the electrolyte may be disposed between the composite article and the second electrode. For example, referring to FIGS. 4A-4C, the electrolyte may be disposed between the composite article (e.g., composite article 100a, 100b, and 100c, respectively) and second electrode 406.

[0121] The electrochemical cell may comprise any of a variety of suitable electrolytes. In certain embodiments, for example, the electrolyte comprises an aqueous electrolyte, an ionic liquid, a solid electrolyte, and / or combinations thereof. Suitable aqueous electrolytes include, but are not limited to, aqueous electrolytes comprising a bicarbonate-containing salt, a hydroxide-containing salt, a chloride-containing salt, an acid, and / or combinations thereof. Other electrolytes and materials are also possible.

[0122] According to certain embodiments, the method may comprise contacting the composite article (e.g., electrode) with the gas and the electrolyte such that the gas diffuses through the layer of the hydrophobic material (e.g., the gas diffusion layer) and contacts the layer of the catalyst material. Referring to FIGS. 4A-4C, for example, the method comprises contacting the composite article (e.g., composite article 100a, 100b, and 100c, respectively) with gas 410 and the electrolyte such gas 410 diffuses through the layer of hydrophobic material 102 and contacts the layer of catalyst material 104.

[0123] The gas may comprise any of a variety of suitable gases. In some embodiments, the gas comprises carbon dioxide (CO2). In certain embodiments, the gas comprises dinitrogen (N2). Other gases are also possible.

[0124] In some embodiments, the method comprises applying a voltage across the electrochemical cell such that the gas contacting the layer of the catalyst material is electrochemically reduced to one or more products. For example, referring to FIGS. 4A-4C, the method comprises applying a voltage across the electrochemical cell (e.g., electrochemical cells 400a, 400b, and 400c, respectively) such that gas 410 contacting the layer of catalyst material 104 is converted to one or more products. According to some embodiments, the conversion of the gas to the one or more products is a reduction of the gas to one or more products.

[0125] The one or more products may comprise any of a variety of suitable products. In certain embodiments, the one or more products are one or more reduction products. For example, in some embodiments wherein the gas comprises CO2, the one or more products comprise greater than or equal to two carbon atoms. In certain embodiments wherein the gas comprises CO2, the one or more products comprise formic acid (HCOOH), carbon monoxide (CO), methane (CF ), methanol (CH3OH), ethylene (C2H4), ethanol (C2H5OH), and / or combinations thereof. In certain embodiments wherein the gas comprises N2, the one or more products comprise ammonia (NH3). Other products are also possible.

[0126] According to certain embodiments, the electrochemical cell is advantageously stable during the application of the voltage across the electrochemical cell. In some embodiments, for example, the voltage of the cell is relatively constant (e.g., within less than or equal to 20%, within less than or equal to 10%, within less than or equal to 5% of the initially applied voltage) over long periods of time.

[0127] The electrochemical cell may be stable during the application of voltage for any of a variety of suitable times. In certain embodiments, for example, the electrochemical cell is stable during the application of the voltage for greater than or equal to 5 hours, greater than or equal to 10 hours, greater than or equal to 50 hours, greater than or equal to 100 hours, greater than or equal to 500 hours, greater than or equal to 1,000 hours, greater than or equal to 5,000 hours, greater than or equal to 10,000 hours, greater than or equal to 20,000 hours, greater than or equal to 30,000 hours, or greater than or equal to 40,000 hours. In some embodiments, the electrochemical cell is stable during the application of the voltage for less than or equal to 50,000 hours, less than or equal to 40,000 hours, less than or equal to 30,000 hours, less than or equal to 20,000 hours, less than or equal to 10,000 hours, less than or equal to 5,000 hours, less than or equal to 1,000 hours, less than or equal to 500 hours, less than or equal to 100 hours, less than or equal to 50 hours, or less than or equal to 5 hours. Combinations of the above recited ranges are possible (e.g., the electrochemical cell is stable during the application of the voltage for greater than or equal to 5 hours and less than or equal to 50,000 hours, the electrochemical cell is stable during the application of the voltage for greater than or equal to 100 hours and less than or equal to 500 hours). Other ranges are also possible.

[0128] According to some embodiments, the faradaic efficiency of the one or more products is advantageously high. As used herein, the faradaic efficiency is given its ordinary meaning in the art and refers to the amount (e.g., moles) of product relative to the amount of product that could be produced from the total charge passed.

[0129] The faradaic efficiency of the one or more products may be any of variety of suitable values. In certain embodiments, for example, the faradaic efficiency of the one or more products is greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, or greater than or equal to 99%. In some embodiments, the faradaic efficiency of the one or more products is less than or equal to 100%, less than or equal to 99%, less than or equal to 90%, less than or equal to 80%, less than or equal to 70%, or less than or equal to 60%. Combinations of the above recited ranges are possible (e.g., the faradaic efficiency of the one or more products is greater than or equal to 50% and less than or equal to 100%, the faradaic efficiency of the one or more products is greater than or equal to 70% and less than or equal to 80%). Other ranges are also possible.

[0130] The faradaic efficiency of ethylene may be any of variety of suitable values. In certain embodiments, for example, the faradaic efficiency of ethylene is greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, or greater than or equal to 99%. In some embodiments, the faradaic efficiency of ethylene is less than or equal to 100%, less than or equal to 99%, less than or equal to 90%, less than or equal to 80%, less than or equal to 70%, or less than or equal to 60%. Combinations of the above recited ranges are possible (e.g., the faradaic efficiency of ethylene is greater than or equal to 50% and less than or equal to 100%, the faradaic efficiency of ethylene is greater than or equal to 70% and less than or equal to 80%). Other ranges are also possible.

[0131] According to certain embodiments, the faradaic efficiency of the one or more products may be measured at a specific current density. The current density of the electrochemical cell may be any of a variety of suitable current densities. In some embodiments, for example, the current density of the electrochemical cell is greater than or equal to 100 mA / cm2, greater than or equal to 200 mA / cm2, greater than or equal to 300 mA / cm2, greater than or equal to 400 mA / cm2, greater than or equal to 500 mA / cm2, greater than or equal to 600 mA / cm2, greater than or equal to 700 mA / cm2, greater than or equal to 800 mA / cm2, greater than or equal to 900 mA / cm2, greater than or equal to 1 A / cm2, greater than or equal to 1.1 A / cm2, greater than or equal to 1.2 A / cm2, greater than or equal to 1.3 A / cm2, greater than or equal to 1.4 A / cm2, greater than or equal to 1.5 A / cm2, greater than or equal to 1.6 A / cm2, greater than or equal to 1.7 A / cm2, greater than or equal to 1.8 A / cm2, or greater than or equal to 1.9 A / cm2. In certain embodiments, the current density of the electrochemical cell is less than or equal to 2 A / cm2, less than or equal to 1.9 A / cm2, less than or equal to 1.8 A / cm2, less than or equal to 1.7 A / cm2, less than or equal to 1.6 A / cm2, less than or equal to 1.5 A / cm2, less than or equal to 1.4 A / cm2, less than or equal to 1.3 A / cm2, less than or equal to 1.2 A / cm2, less than or equal to 1.1 A / cm2, less than or equal to 1 A / cm2, less than or equal to 900 mA / cm2, less than or equal to 800 mA / cm2, less than or equal to 700 mA / cm2, less than or equal to 600 mA / cm2, less than or equal to 500 mA / cm2, less than or equal to 400 mA / cm2, less than or equal to 300 mA / cm2, or less than or equal to 200 mA / cm2. Combinations of the above recited ranges are possible (e.g., the current density of the electrochemical cell is greater than or equal to 100 mA / cm2and less than or equal to 2 A / cm2, the current density of the electrochemical cell is greater than or equal to 900 mA / cm2and less than or equal to 1.1 A / cm2). Other ranges are also possible.

[0132] EXAMPLE 1

[0133] The following examples describes a composite gas diffusion electrode for electrochemical CO2 conversion.

[0134] General Purpose

[0135] To avoid the societal effects of climate change, the 2015 Paris Climate Agreement outlines the reduction of carbon dioxide (CO2) and other greenhouse gas (GHG) emissions to net-zero by mid-century. With global emissions at 39 Gt CCh / year, action should be taken to meet this goal, including carbon capture, sequestration, and utilization. The International Energy Agency (IEA) has outlined energy budgets for a net-zero scenario by 2050, which calls for 7.6 Gt CCh / year carbon capture capacity from point sources and 1.0 Gt CCh / year of direct net-negative CO2 capture from the environment. Direct net-negative capacity in 2021 was just 0.0008 Gt CCh / year, reflecting a need to scale carbon capture technologies.

[0136] Conventional direct carbon capture and carbon capture from point source technologies, however, carry prohibitively high costs. CO2 emissions have historically been treated as a waste stream, meaning that CO2 carries little value in and of itself, thereby causing the economic difficulties faced by CO2 capture operations. A circular economy which uses CO2 as a feedstock rather than a waste product would valorize CO2 and enable economic viability of CO2 capture technologies. In such a cycle, captured CO2 would be used to create valuable chemicals or fuels, which would offset the costs of carbon capture when sold. Such a system would have two-fold benefits, i.e., sequestering CO2 while displacing traditional processes that are dependent on fossil fuel feedstocks.

[0137] Electrochemical CO2 conversion, a technology which could fulfil this vision, is an electrochemical reaction which uses CO2, water, and electrical energy to create up to 16 unique carbon-based products. Some of these products, such as ethylene and ethanol, are valuable and have large markets. Electrochemical CO2 conversion (referred to herein as CO2R, short for CO2 Reduction) has received significant commercial interest in the past years. Although many of the technological performance benchmarks for commercialization have been reached at small scales, integrated implementation at industry-relevant scales has not yet been proven. Herein a composite material is described which enables efficient scaling of the CO2R process architecture to industrial sizes so that the technology can move towards establishing a circular carbon economy.

[0138] Gas Diffusion Laver Background

[0139] Ethylene is chosen as the target chemical for reasons discussed in further detail below. The cathodic half-cell reaction for the electrochemical conversion of CO2 into ethylene is shown in equation 1.

[0140] Fundamentally, CO2R utilizes an aqueous solution which provides the hydrogen ions (or water or hydroxide), a conductive catalyst which provides the electrons, and gaseous CO2. The reaction proceeds on the catalyst, with high concentrations of gaseous CO2 and aqueous ions required for fast reaction rates. Due to the poor solubility of CCh(g) in aqueous solutions, the catalyst must be situated near the triple phase contact line where gas, liquid, and solid phases are all present in close proximity as shown in FIG. 5 A, thereby minimizing the distance that CC>2(aq) must diffuse before reaching the catalyst and ensuring adequate reaction rates. The reaction rate of the process is described by the geometric current density (CD, mA / cm2). The reaction efficiency is in part described by the faradaic efficiency (FE, %), which is the percentage of the total charge transferred that is used for production of a specific compound. High FE’s are desired (ideally 100%) to maintain specificity of the process and reduce separation costs.

[0141] To maintain the spatial proximity of the reactants, a gas diffusion electrode (GDE) architecture is typically employed as shown in FIG. 5B. This architecture consists of a gas diffusion layer (GDL) upon which the catalyst layer is deposited. When hydrophobized, the GDL prevents the impregnation of the aqueous electrolyte beyond the catalyst layer. Such impregnation increases the distance of CO2 diffusion, as the CO2 diffuses through the electrolyte before reaching the catalyst, therefore reducing desired reaction rates and reaction specificity. Impregnation of electrolyte into the GDL, caused by a variety of physicochemical factors, is termed flooding and is a failure mode of CO2R systems. Flooding resistance (or stability) of a GDL is crucial to the viability of CO2R systems, as unstable systems can only maintain peak performance on the order of several hours. Commercial application, however, calls for stability on the order of thousands of hours. Beyond maintaining its hydrophobicity, the GDL should act as a robust physical support for the catalyst layer, allow for ample gaseous CO2 transport to the triple phase contact line, and provide some conductive means of transporting electrons to the catalyst layer to carry out the reaction. Adequate electronic conductivity avoids significant ohmic overpotentials which are a direct cause of electrical inefficiency.

[0142] Conventional Methods, Devices, and Materials

[0143] Conventionally, there are two major GDL architectures. The first, termed a carbon paper GDL, consists of a porous network of carbon fibers that are coated with a thin layer of polytetrafluoroethylene (PTFE) to provide a degree of hydrophobicity. The PTFE coating on carbon paper, however, does not adequately provide robust hydrophobicity to guarantee long term stable performance for CO2R, as the higher required voltages of -0.4 V to -0.8 V vs. RHE cause the carbon paper to lose its hydrophobicity. These systems typically fail due to flooding in tens of hours of high-current density operation. This performance is experimentally demonstrated in FIG. 7, where ethylene FE decreases sharply over just seven hours. The inability to resist flooding precludes efficient operation at scale, as current density is decreased to ensure stability. Even if stability can be obtained with a carbon paper GDL, the range of viable operating conditions are constrained. Carbon paper GDLs have adequate conductivity primarily due to the direction in which they conduct electrons (i.e., through the thickness), as shown in FIG. 6A.

[0144] The second architecture, the expanded polytetrafluoroethylene (ePTFE) GDL, consists of a porous network of pure PTFE fibers. This GDL is robustly hydrophobic due to its pure PTFE nature and has been shown to maintain stable high-current density CO2R to C2+ products for well over 100 hours without failure. However, being composed of pure PTFE, these membranes are electrically insulating, and electrons must be transported to the catalyst through the thin catalyst layer itself. Though efforts have been made to increase the conductivity of these designs, the conductance of these systems typically remains lower than that of carbon paper. The ohmic overpotentials associated with the poor conductance of ePTFE-based GDLs scale with the geometric area of the electrode as shown in FIG. 6B. This causes excessive increases in cell voltage when the electrode area is scaled up, as experimentally demonstrated in FIG. 8. As ohmic losses become significant at scale, FE also decreases dramatically. This inability to scale due to poor conductivity precludes efficient operation at scale.

[0145] Hierarchical Conductive GDE

[0146] In view of the shortcomings described above, a GDL architecture which has both high conductivity as well as robust anti-flooding characteristics is desirable. Described herein is an architecture termed “Hierarchical Conductive GDE” (HCGDE), which utilizes an ePTFE GDL base to maintain strong hydrophobicity and gas diffusion characteristics but carries an additional hierarchically conductive element, placing the HCGDE in the upper right corner of FIG. 9. The conductive elements (e.g., conductors) act as pathways for electrons to travel directly through the GDL with high conductivity before the electrons distribute themselves among the catalyst. This minimizes the distance through which electrons must travel directly along the catalyst layer, thereby drastically reducing the ohmic overpotentials seen in pure ePTFE GDEs. In the hierarchical structure, the conductors act as throughways for electrons to travel freely before reaching their site of reaction through the catalyst layer. The conductors only occupy a small fraction of the total electrode area, therefore minimizing their effect on assembly and flooding resistance.

[0147] Notably, the reorganization of the charge transport mechanism and direction changes the scaling of ohmic overpotentials as shown in FIG. 6C to one which does not scale with the area of the electrode. This indicates that such an electrode should theoretically be able to be scaled to large sizes without aggressive ohmic losses. Rational Design

[0148] According to FIG. 6C, ohmic overpotentials at large electrode sizes are mitigated for small spacings, s, between the conductors. The spacing at which ohmic overpotentials originating from catalyst layer electron transport are no longer important can be estimated via calculations or via simulations. By selecting a bounding overpotential, Vlimit, below which overpotentials are negligible, simple scaling laws for voltage drops can be used to determine the limiting spacing, sUrrdt, as shown in equation 2.

[0149] Alternatively, simulations can be used to predict performance at various spacings, such that given a design target, a limiting spacing can be determined. A COMSOL model was constructed which, given experimentally determined resistivities, calculated the predicted voltage field on an electrode with various spacings. The voltage distribution was converted to a point-wise faradaic efficiency and current density using the performance at small sizes (no ohmic losses) as the ground truth. This model and its accuracy when fitting experimental data is shown in FIGS. 11 A-12D.

[0150] FIGS. 13 A and 13B provide an example of how this simulation can determine the limiting spacing of the conductors. A ‘unit cell’ geometry was simulated whose width reflects the characteristic spacing, schar, of the design. The characteristic spacing was varied and performance metrics were plotted. In FIG. 14, the electrical efficiency (EE) was used, which combines both voltage and faradaic efficiency. The EE was relatively constant at its maximum for characteristic spacings of less than 4 mm. Thus, characteristic spacings of less than 4 mm were selected for subsequent designs.

[0151] Conductor material and sizing is subject to several design considerations. The conductor should not participate detrimentally in the electrochemical reaction, it should have adequate conductivity to avoid ohmic losses within itself, and it should not interfere with assembly of the cell. In some embodiments, the former constraint is satisfied by selecting the conductor material to be the same material as the catalyst. The latter two constraints place bounds on the size and length of the conductor. Thin conductors are preferred to reduce assembly difficulties while larger conductors are preferred to reduce ohmic losses. To rationally design the conductor size and length, the minimum required conductor area, Ac, given the characteristic area, Achar, and a limiting design overpotential was calculated as shown in equation 3.

[0152] Cross-sectional areas above this limit should yield adequately low ohmic losses. HCGDE Experimental Performance

[0153] FIG. 10 shows, according to some embodiments, top-view and cross-sectional schematic diagrams of some exemplary embodiments of HCGDEs. In FIG. 10, lcharrepresents the characteristic length which electrons must travel through the conductor, scharrepresents the characteristic length which electrons must travel through the catalyst layer, and Acharis the characteristic area which one conductor element serves. A sewn configuration of the HCGDE was used for experimental validation of the design. Following equations 2 and 3, the conductor was chosen to be a copper wire of 76 micrometer diameter at a characteristic spacing of approximately 4 mm as suggested by FIG. 14. Such a configuration meets the design requirements described above and is shown in FIGS. 15A and 15B. A test was performed with an electrode size of 4.2 cm2, which showed significantly degraded performance in the absence of hierarchical conductors, as shown in FIGS. 16A and 16B.

[0154] The implementation of the HCGDE reaches the design intent put forth in FIG. 6C, with an ability to scale to larger sizes that are inaccessible to conventional ePTFE GDEs without incurring substantial losses. These improvements are made without sacrificing the robust hydrophobic characteristics associated with the ePTFE membrane used as the GDL. Furthermore, the superior stability of the HCGDE in comparison to a carbon paper GDE is shown in FIG. 17. These developments have made it possible to approach large cell sizes using the HCGDE. A large cell was constructed to test performance at large sizes, as shown in FIG. 18.

[0155] Advantages and Improvements Over Conventional Methods, Devices, and Materials

[0156] Many conventional CO2R processes utilize ePTFE GDEs to reach their peak performance. The hydrophobicity of the ePTFE is crucial to enabling the high current densities, long-term stability, and high faradaic efficiencies. However, the limited conductivity of the ePTFE GDEs limits their ability to scale to larger sizes. Reverting to carbon paper GDEs in order to scale results in a greater flooding constraint, meaning that the same efficiencies and current densities shown at the lab scale with the ePTFE membrane cannot be maintained. Furthermore, carbon paper GDEs struggle to maintain stability, with cells often failing after 5-20 hours of operation.

[0157] The HCGDE described herein enables the transfer of highly stable and high- performance electrodes to large scales without decreases in performance and operational flexibility associated with using carbon paper GDEs, therefore allowing progress larger cells. The ability to scale performance to large sizes, in a way that does not otherwise change or disrupt the behavior of the cell, is an important improvement over conventional systems. The HCGDE configuration can thus easily be directly adapted to most catalysts and cell implementations. Furthermore, it is straightforward modification of the GDE architecture that uses small amounts of low-cost materials. As a mechanical solution, it does not suffer from the complexity of chemical approaches to improve performance.

[0158] Commercial Applications

[0159] CO2R can make a wide array of useful products, including ethylene. Ethylene is the base chemical required for production of all plastics in the world, making it a $230 billion global market and contributing 2% of global CO2 emissions. Ethylene is conventionally produced via high-temperature cracking of fossil fuels and has approximate costs of $1,000 per metric tonne. Should CO2R to ethylene reach cost parity, it could displace conventional methods as a net-negative green alternative. Technoeconomic analyses show that reaching cost parity is feasible if several technology performance parameters (e.g., current density, stability, FE, CO2 utilization) can be met concurrently.

[0160] As described in the previous section, the HCGDE improves performance at scale by maintaining excellent conductivity and hydrophobicity. Beyond increased stability, the most economically compelling advantage of the HCGDE is that it can enable stable operation at elevated current densities in comparison to carbon paper GDEs. As shown in FIG. 19, the maximum stable current density attainable is a crucial aspect of commercialization, as systems with too low of a current density will require infeasibly large total electrode areas and associated CAPEX costs.

[0161] Other industrially developed electrochemical processes utilize electrode areas ranging from 100’s of cm2to as many as multiple meters squared. The current 1-5 cm2scale of conventional GDE systems therefore falls far short of industrially relevant purposes. The HCGDE, with its ability to enable larger electrode sizes, can help to reduce manufacturing costs and make large-scale implementation more feasible.

[0162] Electrochemical CO2R can be used for many other products and pathways, where the benefits provided by the HCGDE architecture are beneficial. For example, generation of carbon monoxide for syngas production and producing ethanol as a renewable fuel are some of many possible applications of the HCGDE.

[0163] EXAMPLE 2

[0164] The following example describes another composite gas diffusion electrode for electrochemical CO2 conversion. Introduction

[0165] Electrochemical CO2 reduction has seen an increase in attention for its promise to convert captured CO2 into a variety of useful fuels, chemicals, and products otherwise produced from petrochemicals. When paired with renewable electricity, CO2 conversion can serve as a means for energy storage or enable net-negative sequestration of CO2 in durable products. Over the last decade, progress in developing novel catalysts, reaction pathways, and electrode architectures have collectively pushed electrochemical CO2 conversion toward the possibility of commercial relevance. However, maintaining lab-scale performance when scaling to commercial sizes poses significant challenges, such as the large-scale production of catalysts and membranes, maintenance of favorable mass and electron transport in larger cells, and thermal management. As CO2 conversion technologies continue to mature, the scalability of electrodes and their supporting systems to large sizes should be taken into consideration.

[0166] A generalized equation for electrochemical reduction of CO2 can be written as shown in equation 4:

[0167] 4) CO2(aq) is provided by a nearby gaseous source due to its poor aqueous diffusivity in order to ensure high reaction rates. Water and / or ions thereof are provided by the presence of a liquid, and the electron is donated by a solid catalyst. Triple phase gas-liquid-solid contact is thereby crucial for maximizing performance of CO2 conversion systems. Gas diffusion electrode (GDE) architectures establish triple phase contact by locating the catalyst layer atop a non-wettable gas diffusion layer (GDL) and have thus become the predominant and highest performing architecture for gaseous phase CO2 conversion. A well-designed GDL should: (i) physically support the catalyst yet must be sufficiently porous for gas transport; (ii) possess adequate electronic conductivity to facilitate electron transport to the catalyst layer with minimal ohmic loss; and (iii) maintain robust hydrophobicity to ensure that the triple phase contact is sustained close to the catalyst. The simultaneous requirement of robust hydrophobicity and good conductivity presents a challenging design tradeoff. Generally, there exists a negative correlation between hydrophobicity and conductivity for engineering materials commonly used in GDEs: highly conductive materials tend to be hydrophilic, and the most hydrophobic materials tend to be nonconductive. The ramifications of this fundamental tradeoff are readily apparent in the GDLs employed in today’s conventional CO2 conversion systems.

[0168] One of the most common GDLs is carbon paper, consisting of carbon fibers coated in PTFE. Carbon paper has good conductivity, allowing electrons to conduct directly through the thickness of the GDL to reach the catalyst as shown in FIG. 6A. Given a square electrode with side length L and area A = L2, a current density i, a carbon paper thickness tc, and an effective resistivity of the carbon pc, the ohmic losses through the GDL can be estimated as shown in equation 5:

[0169] AF ~ iAR ~ ipctc(eq.

[0170] 5)

[0171] Because carbon paper has good conductivity and the ohmic losses are not a function of the electrode area, scaling to large carbon paper electrode sizes does not incur significant ohmic losses. However, carbon paper electrodes are known to lose their hydrophobicity during operation due to PTFE coating degradation among many other physical mechanisms. Carbon paper is therefore susceptible to flooding events, in which the electrolyte impregnates the GDL, increasing the diffusion distance of CO2(aq), and reducing CO2 conversion rates and specificity. This flooding instability of carbon paper was experimentally demonstrated in FIG. 7, in which ethylene selectivity decreases and hydrogen evolution increases over several hours. Such approaches to prevent flooding on carbon paper, including constant re- hydrophobization of the GDE, meticulously balancing the relative pressures, modifying the catalyst or catalyst layer, and controlling pore size distributions, are difficult to sustain over long periods and significantly constrain the operational freedom of these systems.

[0172] Another GDL which has gained popularity in recent years for its ability to resist flooding is expanded polytetrafluoroethylene (ePTFE). It is composed of a porous network of pure PTFE fibers and thus has very robust hydrophobicity. Its superior stability and hydrophobicity has led to its frequent use in the highest performing electrodes. However, PTFE is no exception to the aforementioned intrinsic material tradeoff between hydrophobicity and conductivity: it is an excellent electrical insulator, with a conductivity on the order of 10'16S / m. Electrons cannot be transported through ePTFE GDLs, forcing the catalyst layer itself to facilitate in-plane electron transport as shown in FIG. 6B. The change in directionality of electron transport fundamentally changes the scaling of ohmic losses in the electrode. With tcatas the thickness and pcatas the effective resistivity of the catalyst layer, we calculate the ohmic losses again for the ePTFE configuration in FIG. 6B as shown in equation 6:

[0173] It was observed that the ohmic losses scale through the catalyst layer as a function of the electrode area, L2. Critically, this indicates that ohmic losses will become increasingly problematic as the technology progresses to commercialization and the electrode size increases. Adding carbon and graphite atop the catalyst layer to increase conductivity does not overcome the fundamental direction of electron transport and thus the adverse scaling behavior. For this reason, implementations of PTFE electrodes to date have been constrained to electrode areas of <5 cm2.

[0174] Electrodes of such limited size are not feasible for commercial implementation, as the immense number of cells would incur extensive balance of plant costs. For example, there are other electrochemical applications that contextualize a reasonable electrode size which reconciles balance of plant, fabrication costs, and operational costs associated with electrode performance. Proton exchange membrane (PEM) electrolysis installations ranging from several kW to several megawatts have electrode sizes from 300 cm2to 3000 cm2. Even more advanced technologies like fuel cells and chlor-alkali electrolyzers have electrode areas of 10,000 cm2or greater. It was thus concluded that ePTFE electrodes of several cm2are infeasible to scale. The resolution of the ePTFE electrode conductivity bottleneck is therefore of critical importance to ensure that this highly performing electrode architecture can be scaled to commercial relevance.

[0175] The performance of ePTFE electrodes at increasing electrode sizes has not been explored in depth, leaving the length scales at which such ohmic losses become relevant unknown. Moreover, there is a distinct opportunity to design a new family of GDE architectures consisting of composite GDLs which possess both excellent hydrophobicity and conductivity, as shown conceptually in FIG. 9. In this example, the fundamental underpinnings of ohmic losses in ePTFE-based electrodes are explored, and a hierarchically conductive composite electrode architecture is designed and validated. The hierarchically conductive composite electrode reaches -75% C2+ faradaic efficiency (FE) at a current density of 200mA / cm2and an electrode size of 50 cm2. Scaling of ePTFE Electrodes

[0176] Conventional ePTFE cathodes were fabricated with a 250 nm thick copper catalyst deposited on an ePTFE membrane with 450 nm pores. The cathodes were assembled in a Membrane Electrode Assembly (MEA) along with an iridium oxide carbon paper anode, separated by a Dioxide Materials anion exchange membrane for ion migration.

[0177] To assess the effects of ePTFE electrode size on performance, three square electrodes of sizes 0.5 cm2, 2.5 cm2, and 4.2 cm2were evaluated for their ethylene productivity, with results shown in FIG. 8. The 0.5 cm2electrode performs well, achieving 47% FE towards ethylene and an estimated 84% FE towards C2+ products at an industrially relevant current density of 200 mA / cm2. However, the 4.2 cm2electrode exhibits a substantially reduced peak ethylene FE of 29% and a full cell voltage at 200 mA / cm2which is 0.81 V greater than the 0.5 cm2electrode at the same current density. Clearly, the effects of scale on ePTFE electrode performance are drastic even at single cm2, lending credence to the size limitation and further motivating the development of novel GDE architectures with simultaneous hydrophobicity and conductivity.

[0178] To this end, a novel GDE architecture is described herein that supplements ePTFE electrodes with additional hierarchical conducting elements as shown in FIG. 6C. This approach makes good use of the inherent hydrophobicity of ePTFE membranes, requiring only the improvement of conductivity. To rationally approach the conductivity challenge, the fundamental effects driving the observed voltage increase and selectivity decrease should be understood.

[0179] Rationalizing Declining Performance at Scale The increasing cell voltage with increasing electrode size is readily accounted for by the ohmic losses through the catalyst layer expressed in equation 6. On the other hand, the mechanism behind decreasing product selectivities was not as immediately clear. Noting that different products begin to be produced at different overpotentials (CO, then C2+, then H2, from low to high overpotential), it was hypothesized that when ohmic losses reach a similar order as these overpotentials, there can exist significant spatial gradients in overpotential and thus product generation, leading to decreased overall selectivity. This is shown conceptually in FIG. 20A, wherein the left side of the electrode closest to the electrical connection has the highest absolute overpotential and is expected to exhibit a greater degree of hydrogen evolution. Conversely, the right side has a lower absolute overpotential due to significant ohmic voltage drops and is expected to produce predominantly CO. To experimentally validate this phenomenon, a new reactor with three independent serpentine flow paths designed and fabricated, each flow path aligned with a third of the electrode as denoted / , II, and / / / in FIG. 20A. The local product distributions of each of the three sectors shown in FIG. 20B match the hypothesis, with sector / producing more hydrogen and sector / / / producing more CO.

[0180] A model was then developed to confirm the role of ohmic effects, knowing the model could subsequently be used as a design tool to predict the performance of proposed electrode designs. Briefly, a 2-D finite element model was constructed which iteratively computed the non-Laplacian voltage field on the electrode by coupling Ohm’s law and current conservation given the out-of-plane current which contributes to the electrochemical reaction. The pointwise electrochemical current was estimated as a function of the voltage by using the experimental data of the 0.5 cm2electrode in which ohmic losses are minimal and thus the entire electrode can be considered equipotential. A representative simulated voltage field is shown in FIG. 11 A.

[0181] To validate the accuracy of the model, a 4.2 cm2electrode was simulated using only the reference performance at 0.5 cm2. As expected, the voltage and ethylene FE are shown to have significant spatial variations as shown in FIGS. 11 A and 1 IB. The modelled performance and experimental results present a strong match as shown in FIGS. 12A and 12B. The model captures the increased cell voltages at 4.2 cm2, as well as the decreased peak FE and the shift in peak FE voltage. The ability of this model to predict performance of larger electrodes while only accounting for the ohmic losses in the catalyst layer confirms the central role which insufficient conductivity plays in the limited performance of ePTFE electrodes. HCGDE Experimental Performance

[0182] To design a new electrode architecture with improved electron transport, inspiration was drawn from natural and engineered systems which leverage hierarchy to optimize transport. Efficient transport systems of all kinds, from the cardiovascular system to public transport networks, hold in common the use of large, high volume transport passages for long distance transport, with progressively smaller branching passages enabling medium-distance and then short-distance transport to the destination. By observing the journey of an electron in a conventional ePTFE electrode, the shortcomings of its design with respect to hierarchy were readily recognized. An electron first travels several centimeters through a current collector of millimetric thickness. It must then travel several centimeters through the catalyst layer only hundreds of nanometers thick. As evidenced by the ohmic losses, the sub-micron catalyst layer does not have sufficient capacity (conductance) to facilitate centimetric electron transport. To alleviate this bottleneck, a micrometric conductor was introduced into the GDL to bridge the conduction from the underlying current collector to the sub-micron catalyst layer. The micrometric conductor facilitates medium-range distribution of electrons within the catalyst layer, limiting the sub-micron transport to distances small enough to prevent significant ohmic losses. The GDE architecture with conducting elements across lengthscales is described herein as the Hierarchically Conductive GDE (HCGDE).

[0183] The HCGDE embodiment shown in FIG. 21 features a micrometric copper wire which pierces the ePTFE membrane and runs along the catalyst layer. The wire connects to the current collector on the backside of the GDL. To determine the wire spacing for which ohmic losses in the catalyst layer become negligible, the previously validated model was used as a design tool. In FIG. 22, a representative simulation result of a wire design unit cell is shown, with equipotential current source regions representing the wires at the top and bottom edges. The wire spacing is swept from one to one hundred millimeters, and the spatially averaged FE is presented in FIG. 14. From these results, it was reasoned that the HCGDEs should maintain sufficient conductivity and minimize ohmic losses through the catalyst layer when wire spacing is held below 4 mm.

[0184] For the HCGDE design to remain practical, the micrometric conductive elements should not otherwise negatively affect the electrode or overall cell architecture. Copper was chosen as the wire material for its high conductivity and because it matches the catalyst material, reducing the likelihood of parasitic electrochemical reactions. Moreover, a 75 micrometer diameter copper wire at 4 mm spacing will occupy less than 2% of the electrode surface, negligibly decreasing the active surface area. Though some small degree of liquid penetration may occur in the microscopic holes required for the penetration of the wire, the flooding will be limited to this region by the robust hydrophobicity of the surrounding ePTFE. Thus, it was expected that the HCGDE should maintain the same degree of stability as ePTFE electrodes. The piercing wire embodiment is also simple and highly scalable, as it can be fabricated roll-to-roll with classic sewing techniques.

[0185] To evaluate the HCGDE performance, 14 cm2and 50 cm2electrodes were fabricated with the previously described ePTFE electrodes as a base, additionally sewing 75 micrometer diameter wires into the GDEs at 4 mm spacing. A 50 cm2MEA pilot scale reactor was constructed to execute performance tests. Upon assembly and disassembly of the wire HCGDE, no differences or damage to the membrane, electrodes, or electrolyzer were observed due to the flexibility and small profile of the 75 micrometer wires. FIGS. 23-24B demonstrate how the HCGDE overcomes the conductivity limitations of ePTFE electrodes, enabling high performance at large scales. As the electrode size is increased a full two orders of magnitude from 0.5 cm2to 50 cm2, the full cell voltage is unchanged: the full cell potential of the 0.5 cm2electrode is 3.58 V to reach 200 mA / cm2, while the full cell potential of the 50 cm2electrode is 3.52 V. Moreover, C2+ product FEs remain at about 75% for large electrode sizes up to 50.0 cm2, leading to a sustained electrical efficiency (EE) of -25% up to the 50 cm2size. The HCGDE outperforms the modeled 50 cm2ePTFE electrode, producing more ethylene and attaining higher current densities at substantially lower voltages, despite the tendency of the model to overpredict FE. The 100 cm2ePTFE electrode performance demonstrates that scaling issues become more severe at larger, more commercially relevant electrode sizes. The HCGDE electrode is stable, and no flooding is observed over the course of a 10 hour stability test.

[0186] Discussion and Conclusion

[0187] The HCGDE platform employs hierarchical charge conduction to eliminate the ohmic losses which afflict conventional ePTFE electrodes, enabling low voltages and high electrochemical CO2 reduction faradaic efficiencies at pilot scale. The improvement of conductivity is achieved with a minimal footprint (<2% area) and without sacrificing the bulk hydrophobicity of the ePTFE. The HCGDE simultaneously achieves excellent hydrophobicity and good conductivity, reaching the upper right comer of FIG. 9. The physical HCGDE approach can be implemented in any existing GDE and can enable scaling of electrodes independent of their catalyst composition or morphology. Moreover, by decoupling the electron conduction and hydrophobicity requirements of the GDL, this approach unlocks entirely new electrode architecture design spaces. This example demonstrates with models and experiments how conventionally employed ePTFE electrodes fail to maintain their performance at larger electrode sizes due to their poor in-plane conductivity. To this end, a hierarchical design framework was leveraged to design a HCGDE which introduces micrometric wires within the GDL to effectively distribute electrons across the electrode and alleviate ohmic losses. The ability of the HCGDE technique to maintain performance at scale is demonstrated with a 50 cm2reactor. This approach is simple, low-impact, and flexible, and can readily be applied to existing high performing catalysts to enable their immediate scaling with a robust GDE. The HCGDE platform achieves simultaneously excellent bulk hydrophobicity and good conductivity, thereby unlocking the design space of GDLs and relieving constraints on system operational parameters. Methods

[0188] Electrode preparation: To fabricate the ePTFE cathodes, magnetron sputtering (AJA International) was used to deposit 250 nm of copper on a 450 nm pore size Aspire Laminated PTFE membrane (Sterlitech) at a rate of 0.83 A / s, calibrated via Quartz Crystal Monitor (QCM). HCGDEs were fabricated by punching holes on the edges of the base ePTFE cathodes with a needle and threading a 75 micrometer diameter copper wire through the holes. A piece of copper foil (25 micrometers) was wrapped around the very edge of ePTFE electrodes to establish electrical connection to the flowfield current collector. Iridium oxide on carbon paper anodes were purchased from Dioxide Materials and cut to size.

[0189] Electrochemical testbeds: All electrochemical tests were performed in Membrane Electrode Assemblies (MEA) with a graphite cathodic serpentine flowfield and a titanium anodic serpentine flowfield. Experiments with electrodes <5 cm2were performed in a MEA with 5 cm2flowfield area, experiments with electrodes >5 cm2were performed in an MEA with 50 cm2flowfield area. The anode and cathode were separated by an anion exchange membrane (Sustainion X37-50, Dioxide Materials). The anode was surrounded by a 0.25 mm thick PTFE gasket, while the cathode was placed atop a 25 micrometer thick PTFE gasket cut with a square open area of the appropriate active area. CO2 (99.995%, Airgas) was humidified and flowed through the cathode flowfield at 160 SCCM (50 cm2electrode) or 100 SCCM (all other experiments). 10 mM KHCO3 was recirculated in the anode at 60 mL / min from a 200 mL reservoir with a peristaltic pump in all experiments. Cell temperature was measured continuously with a thermocouple and was confirmed to remain in the range of 25° C to 30° C for all experiments. All experiments were chronopotentiometric, progressing from low to high current density (10, 50, 100, 150, 200, 250, 300 mA / cm2) and holding for 14 minutes at each current density. For electrodes <5 cm2, the current was supplied and full cell voltage was measured with a BioLogic SP-150 Potentiostat. For electrodes >5 cm2, the current was supplied by a power supply (TDK-Lambda GEN300-17) due to the maximum current limitations of the potentiostat. The full cell voltage was measured with the potentiostat.

[0190] Product Characterization: Gas products were quantified with a Gas Chromatograph (Agilent 7890B) calibrated with a custom gas precision mixture (Gasco and Shopcross). Liquid products were collected from both the anode electrolyte and a cold trap placed after the cathode, and were measured with Nuclear Magnetic Resonance (NMR) (Brucker 402) with DMSO and Phenol in D2O standard.

[0191] While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present invention is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present invention.

[0192] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0193] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0194] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0195] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0196] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[0197] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMSWhat is claimed is:

1. A composite article, comprising: a hydrophobic material having a water contact angle of greater than or equal to 90°; a catalyst material; and an electrically conductive material having an electrical conductivity of greater than or equal to 104S / m, wherein the electrically conductive material occupies less than or equal to 5% of a surface area of the catalyst material.

2. The composite article of claim 1, wherein the water contact angle of the hydrophobic material is less than or equal to 180°.

3. The composite article of any one of claims 1-2, wherein the hydrophobic material is configured as a layer.

4. The composite article of claim 3, wherein the layer of the hydrophobic material has a thickness of greater than or equal to 1 micrometer and less than or equal to 1 millimeter.

5. The composite article of any one of claims 1-4, wherein the hydrophobic material comprises a plurality of pores.

6. The composite article of claim 5, wherein the plurality of pores have an average characteristic dimension of greater than or equal to 0.01 micrometers and less than or equal to 10 micrometers.

7. The composite article of any one of claims 1-6, wherein the hydrophobic material is electrically insulating.

8. The composite article of any one of claims 1-7, wherein the hydrophobic material comprises polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), and / or combinations thereof.

9. The composite article of any one of claims 1-8, wherein the catalyst material is configured as a layer.

10. The composite article of claim 9, wherein the layer of the catalyst material has a thickness of greater than or equal to 1 nanometer and less than or equal to 20 micrometers.

11. The composite article of any one of claims 1-10, wherein the catalyst material comprises a metal.

12. The composite article of any one of claims 1-11, wherein the catalyst material comprises copper (Cu), silver (Ag), gold (Au), zinc (Zn), and / or combinations thereof.

13. The composite article of any one of claims 1-12, wherein the electrical conductivity of the electrically conductive material is less than or equal to 108S / m ohm / m.

14. The composite article of any one of claims 1-13, wherein the electrically conductive material occupies less than or equal to 2% of the surface area of the catalyst material.

15. The composite article of any one of claims 1-14, wherein the electrically conductive material occupies greater than or equal to 1% of the surface area of the catalyst material.

16. The composite article of any one of claims 1-15, wherein the electrically conductive material comprises Cu, Ag, and / or combinations thereof.

17. The composite article of any one of claims 1-16, wherein the composite article comprises a plurality of electrically conductive materials.

18. The composite article of claim 17, wherein the plurality of electrically conductive materials are discontinuous such that each electrically conductive material in the plurality of electrically conductive materials has a characteristic spacing from a neighboring electrically conductive material in the plurality of electrically conductive materials.

19. An electrode, comprising:a catalyst layer having a first surface and a second surface, wherein the first surface is substantially opposite the second surface; a gas diffusion layer disposed on the second surface of the catalyst layer; and an electrically conductive material, wherein at least a portion of the electrically conductive material is configured to be in electrical communication with a current collector such that the electrically conductive material provides an electrically conductive pathway from the current collector to the first surface of the catalyst layer, wherein the electrode has a geometric area greater than or equal to 5 cm2.

20. The electrode of claim 19, wherein the gas diffusion layer is hydrophobic.

21. The electrode of any one of claims 19-20, wherein the gas diffusion layer has a water contact angle of greater than or equal to 90° and less than or equal to 180°.

22. The electrode of any one of claims 19-21, wherein a thickness of the gas diffusion layer is greater than or equal to 1 micrometer and less than or equal to 1 millimeter.

23. The electrode of any one of claims 19-22, wherein the gas diffusion layer comprises a plurality of pores having an average characteristic dimension of greater than or equal to 0.01 micrometers and less than or equal to 10 micrometers.

24. The electrode of any one of claims 19-23, wherein the gas diffusion layer is electrically insulating.

25. The electrode of any one of claims 19-24, wherein the gas diffusion layer comprises polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), and / or combinations thereof.

26. The electrode of any one of claims 19-25, a thickness of the catalyst layer is greater than or equal to 1 nanometer and less than or equal to 20 micrometers.

27. The electrode of any one of claims 19-26, wherein the catalyst layer comprises Cu, Ag, Au, Zn, and / or combinations thereof.

28. The electrode of any one of claims 19-27, wherein the electrically conductive material has an electrical conductivity of greater than or equal to 104S / m and less than or equal to 108S / m.

29. The electrode of any one of claims 22-28, wherein at least a portion of the electrically conductive pathway from the current collector to the first surface of the catalyst layer travels through the thickness of the gas diffusion layer.

30. The electrode of any one of claims 22-28, wherein at least a portion of the electrically conductive pathway from the current collector to the first surface of the catalyst layer does not travel through the thickness of the gas diffusion layer.

31. The electrode of any of claims 26-30, wherein at least a portion of the electrically conductive pathway from the current collector to the first surface of the catalyst layer travels through the thickness of the catalyst layer.

32. The electrode of any one of claims 26-30, wherein at least a portion of the electrically conductive pathway from the current collector to the first surface of the catalyst layer does not travel through the thickness of the catalyst layer.

33. The electrode of any one of claims 19-32, wherein the geometric area of the electrode is greater than or equal to 50 cm2.

34. The electrode of any one of claims 19-33, wherein the geometric area of the electrode is greater than or equal to 1,000 cm2.

35. The electrode of any one of claims 19-34, wherein the geometric area of the electrode is less than or equal to 10,000 cm2.

36. The electrode of any one of claims 19-35, wherein the electrode is a gas diffusion electrode.

37. The electrode of any one of claims 19-36, wherein the electrode comprises a plurality of electrically conductive materials.

38. The electrode of claim 37, wherein the plurality of electrically conductive materials are discontinuous such that each electrically conductive material in the plurality of electrically conductive materials has a characteristic spacing from a neighboring electrically conductive material in the plurality of electrically conductive materials.

39. An electrochemical cell comprising: the electrode of any one of claims 19-38; and the current collector.

40. The electrochemical cell of claim 39, wherein the electrode is a first electrode and the current collector is a first current collector, and wherein the electrochemical cell further comprises a second electrode and a second current collector.

41. A catalytic, aqueous barrier, gas diffusion electrode, comprising: a hydrophobic gas diffusion layer configured to provide a substantial barrier to transport of an electrolyte across the electrode from a first surface of the electrode to a second surface of the electrode, wherein the second surface of the electrode is substantially opposite the first surface, and wherein the electrode has a gas permeability of at least 0.05 f / min ft2at 125 Pa across at least a portion of the electrode and a water entry pressure of less than 100 psi across at least a portion of the electrode; a catalyst material configured to be exposed to the electrolyte in contact with the first surface of the electrode; and an electrically conductive material configured to provide electronic conductivity to at least some of the catalyst material, wherein the catalyst material is configured to be in contact with a gas in the electrolyte in contact with the first surface of the electrode, the electrically conductive material configured to be in electrical communication with a current collector in contact with the second surface of the electrode such that the electrically conductive material provides an electrically conductive pathway from the current collector to the catalyst material.

42. The catalytic, aqueous barrier, gas diffusion electrode of claim 41, wherein the gas permeability of the electrode is less than or equal to 8 ft3 / min ft2at 125 Pa across at least the portion of the electrode.

43. The catalytic, aqueous barrier, gas diffusion electrode of any one of claims 41-42, wherein the water entry pressure of the electrode is greater than or equal to 0.05 psi across at least the portion of the electrode.

44. A method of electrochemically converting a gas to one or more products, comprising: providing the electrochemical cell of any one of claims 39-40; contacting the electrode with the gas and an electrolyte such that the gas diffuses through the gas diffusion layer and contacts the catalyst layer; and applying a voltage across the electrochemical cell such that the gas contacting the catalyst layer is electrochemically converted to the one or more products.

45. The method of claim 44, wherein the gas contacting the catalyst layer is electrochemically reduced to one or more products.

46. The method of any one of claims 44-45, wherein the gas comprises carbon dioxide (CO2).

47. The method of any one of claims 44-46, wherein the one or more products comprise greater than or equal to two carbon atoms.

48. The method of any one of claims 44-46, wherein the one or more products comprise formic acid (HCOOH), carbon monoxide (CO), methane (CH4), methanol (CH3OH), ethylene (C2H4), ethanol (C2H5OH), and / or combinations thereof.

49. The method of any one of claims 44-48, wherein the gas comprises dinitrogen (N2).

50. The method of any one of claims 44-49, wherein the one or more products comprise ammonia (NH3).

51. The method of any one of claims 44-50, wherein the electrochemical cell is stable during the application of the voltage for greater than or equal to 5 hours and less than or equal to 50,000 hours.

52. The method of any one of claims 44-51, wherein a faradaic efficiency of the one or more products is greater than or equal to 50% and less than or equal to 100% at a current density of greater than or equal to 100 mA / cm2and less than or equal to 2 A / cm2.

53. The method of any one of claims 44-52, wherein the electrolyte comprises an aqueous electrolyte, an ionic liquid, a solid electrolyte, and / or combinations thereof.

54. The method of claim 53, wherein the aqueous electrolyte comprises a bicarbonate- containing salt, a hydroxide-containing salt, a chloride-containing salt, an acid, and / or combinations thereof.

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